Support for Xtensa emitter and assembler, and upgraded F4 and F7 STM HAL

This release adds support for the Xtensa architecture as a target for the
native emitter, as well as Xtensa inline assembler.  The int.from_bytes
and int.to_bytes methods now require a second argument (the byte order)
per CPython (only "little" is supported at this time).  The "readall"
method has been removed from all stream classes that used it; "read" with
no arguments should be used instead.  There is now support for importing
packages from compiled .mpy files.  Test coverage is increased to 96%.

The generic I2C driver has improvements: configurable clock stretching
timeout, "stop" argument added to readfrom/writeto methods, "nack"
argument added to readinto, and write[to] now returns num of ACKs
received.  The framebuf module now handles 16-bit depth (generic colour
format) and has hline, vline, rect, line methods.  A new utimeq module is
added for efficient queue ordering defined by modulo time (to be
compatible with time.ticks_xxx functions).  The pyboard.py script has been
modified so that the target board is not reset between scripts or commands
that are given on a single command line.

For the stmhal port the STM Cube HAL has been upgraded: Cube F4 HAL to
v1.13.1 (CMSIS 2.5.1, HAL v1.5.2) and Cube F7 HAL to v1.1.2.  There is a
more robust pyb.I2C implementation (DMA is now disabled by default, can be
enabled via an option), and there is an implementation of machine.I2C with
robust error handling and hardware acceleration on F4 MCUs.  It is now
recommended to use machine.I2C instead of pyb.I2C.  The UART class is now
more robust with better handling of errors/timeouts.  There is also more
accurate VBAT and VREFINT measurements for the ADC.  New boards that are
supported include: NUCLEO_F767ZI, STM32F769DISC and NUCLEO_L476RG.

For the esp8266 port select/poll is now supported for sockets using the
uselect module.  There is support for native and viper emitters, as well
as an inline assembler (with limited iRAM for storage of native functions,
or the option to store code to flash).  There is improved software I2C
with a slight API change: scl/sda pins can be specified as positional only
when "-1" is passed as the first argument to indicate the use of software
I2C.  It is recommended to use keyword arguments for scl/sda.  There is
very early support for over-the-air (OTA) updates using the yaota8266
project.

A detailed list of changes follows.

py core:
- emitnative: fix native import emitter when in viper mode
- remove readall() method, which is equivalent to read() w/o args
- objexcept: allow clearing traceback with 'exc.__traceback__ = None'
- runtime: mp_resume: handle exceptions in Python __next__()
- mkrules.mk: rework find command so it works on OSX
- *.mk: replace uses of 'sed' with $(SED)
- parse: move function to check for const parse node to parse.[ch]
- parse: make mp_parse_node_new_leaf an inline function
- parse: add code to fold logical constants in or/and/not operations
- factor persistent code load/save funcs into persistentcode.[ch]
- factor out persistent-code reader into separate files
- lexer: rewrite mp_lexer_new_from_str_len in terms of mp_reader_mem
- lexer: provide generic mp_lexer_new_from_file based on mp_reader
- lexer: rewrite mp_lexer_new_from_fd in terms of mp_reader
- lexer: make lexer use an mp_reader as its source
- objtype: implement __call__ handling for an instance w/o heap alloc
- factor out common code from assemblers into asmbase.[ch]
- stream: move ad-hoc ioctl constants to stream.h and rename them
- compile: simplify configuration of native emitter
- emit.h: remove long-obsolete declarations for cpython emitter
- move arch-specific assembler macros from emitnative to asmXXX.h
- asmbase: add MP_PLAT_COMMIT_EXEC option for handling exec code
- asmxtensa: add low-level Xtensa assembler
- integrate Xtensa assembler into native emitter
- allow inline-assembler emitter to be generic
- add inline Xtensa assembler
- emitinline: embed entire asm struct instead of a pointer to it
- emitinline: move inline-asm align and data methods to compiler
- emitinline: move common code for end of final pass to compiler
- asm: remove need for dummy_data when doing initial assembler passes
- objint: from_bytes, to_bytes: require byteorder arg, require "little"
- binary: do zero extension when storing a value larger than word size
- builtinimport: support importing packages from compiled .mpy files
- mpz: remove unreachable code in mpn_or_neg functions
- runtime: zero out fs_user_mount array in mp_init
- mpconfig.h: enable MICROPY_PY_SYS_EXIT by default
- add MICROPY_KBD_EXCEPTION config option to provide mp_kbd_exception
- compile: add an extra pass for Xtensa inline assembler
- modbuiltins: remove unreachable code
- objint: rename mp_obj_int_as_float to mp_obj_int_as_float_impl
- emitglue: refactor to remove assert(0), to improve coverage
- lexer: remove unreachable code in string tokeniser
- lexer: remove unnecessary check for EOF in lexer's next_char func
- lexer: permanently disable the mp_lexer_show_token function
- parsenum: simplify and generalise decoding of digit values
- mpz: fix assertion in mpz_set_from_str which checks value of base
- mpprint: add assertion for, and comment about, valid base values
- objint: simplify mp_int_format_size and remove unreachable code
- unicode: comment-out unused function unichar_isprint
- consistently update signatures of .make_new and .call methods
- mkrules.mk: add MPY_CROSS_FLAGS option to pass flags to mpy-cross
- builtinimport: fix bug when importing names from frozen packages

extmod:
- machine_i2c: make the clock stretching timeout configurable
- machine_i2c: raise an error when clock stretching times out
- machine_i2c: release SDA on bus error
- machine_i2c: add a C-level I2C-protocol, refactoring soft I2C
- machine_i2c: add argument to C funcs to control stop generation
- machine_i2c: rewrite i2c.scan in terms of C-level protocol
- machine_i2c: rewrite mem xfer funcs in terms of C-level protocol
- machine_i2c: remove unneeded i2c_write_mem/i2c_read_mem funcs
- machine_i2c: make C-level functions return -errno on I2C error
- machine_i2c: add 'nack' argument to i2c.readinto
- machine_i2c: make i2c.write[to] methods return num of ACKs recvd
- machine_i2c: add 'stop' argument to i2c readfrom/writeto meths
- machine_i2c: remove trivial function wrappers
- machine_i2c: expose soft I2C obj and readfrom/writeto funcs
- machine_i2c: add hook to constructor to call port-specific code
- modurandom: allow to build with float disabled
- modframebuf: make FrameBuffer handle 16bit depth
- modframebuf: add back legacy FrameBuffer1 "class"
- modframebuf: optimise fill and fill_rect methods
- vfs_fat: implement POSIX behaviour of rename, allow to overwrite
- moduselect: use stream helper function instead of ad-hoc code
- moduselect: use configurable EVENT_POLL_HOOK instead of WFI
- modlwip: add ioctl method to socket, with poll implementation
- vfs_fat_file: allow file obj to respond to ioctl flush request
- modbtree: add method to sync the database
- modbtree: rename "sync" method to "flush" for consistency
- modframebuf: add hline, vline, rect and line methods
- machine_spi: provide reusable software SPI class
- modframebuf: make framebuf implement the buffer protocol
- modframebuf: store underlying buffer object to prevent GC free
- modutimeq: copy of current moduheapq with timeq support for refactoring
- modutimeq: refactor into optimized class
- modutimeq: make time_less_than be actually "less than", not less/eq

lib:
- utils/interrupt_char: use core-provided mp_kbd_exception if enabled

drivers:
- display/ssd1306.py: update to use FrameBuffer not FrameBuffer1
- onewire: enable pull up on data pin
- onewire/ds18x20: fix negative temperature calc for DS18B20

tools:
- tinytest-codegen: blacklist recently added uheapq_timeq test (qemu-arm)
- pyboard.py: refactor so target is not reset between scripts/cmd
- mpy-tool.py: add support for OPT_CACHE_MAP_LOOKUP_IN_BYTECODE

tests:
- micropython: add test for import from within viper function
- use read() instead of readall()
- basics: add test for logical constant folding
- micropython: add test for creating traceback without allocation
- micropython: move alloc-less traceback test to separate test file
- extmod: improve ujson coverage
- basics: improve user class coverage
- basics: add test for dict.fromkeys where arg is a generator
- basics: add tests for if-expressions
- basics: change dict_fromkeys test so it doesn't use generators
- basics: enable tests for list slice getting with 3rd arg
- extmod/vfs_fat_fileio: add test for constructor of FileIO type
- extmod/btree1: exercise btree.flush()
- extmod/framebuf1: add basics tests for hline, vline, rect, line
- update for required byteorder arg for int.from_bytes()/to_bytes()
- extmod: improve moductypes test coverage
- extmod: improve modframebuf test coverage
- micropython: get heapalloc_traceback test running on baremetal
- struct*: make skippable
- basics: improve mpz test coverage
- float/builtin_float_round: test round() with second arg
- basics/builtin_dir: add test for dir() of a type
- basics: add test for builtin locals()
- basics/set_pop: improve coverage of set functions
- run-tests: for REPL tests make sure the REPL is exited at the end
- basics: improve test coverage for generators
- import: add a test which uses ... in from-import statement
- add tests to improve coverage of runtime.c
- add tests to improve coverage of objarray.c
- extmod: add test for utimeq module
- basics/lexer: add a test for newline-escaping within a string
- add a coverage test for printing the parse-tree
- utimeq_stable: test for partial stability of utimeq queuing
- heapalloc_inst_call: test for no alloc for simple object calls
- basics: add tests for parsing of ints with base 36
- basics: add tests to improve coverage of binary.c
- micropython: add test for micropython.stack_use() function
- extmod: improve ubinascii.c test coverage
- thread: improve modthread.c test coverage
- cmdline: improve repl.c autocomplete test coverage
- unix: improve runtime_utils.c test coverage
- pyb/uart: update test to match recent change to UART timeout_char
- run-tests: allow to skip set tests
- improve warning.c test coverage
- float: improve formatfloat.c test coverage using Python
- unix: improve formatfloat.c test coverage using C
- unix/extra_coverage: add basic tests to import frozen str and mpy
- types1: split out set type test to set_types
- array: allow to skip test if "array" is unavailable
- unix/extra_coverage: add tests for importing frozen packages

unix port:
- rename define for unix moduselect to MICROPY_PY_USELECT_POSIX
- Makefile: update freedos target for change of USELECT config name
- enable utimeq module
- main: allow to print the parse tree in coverage build
- Makefile: make "coverage_test" target mirror Travis test actions
- moduselect: if file object passed to .register(), return it in .poll()
- Makefile: split long line for coverage target, easier to modify
- enable and add basic frozen str and frozen mpy in coverage build
- Makefile: allow cache-map-lookup optimisation with frozen bytecode

windows port:
- enable READER_POSIX to get access to lexer_new_from_file

stmhal port:
- dma: de-init the DMA peripheral properly before initialising
- i2c: add option to I2C to enable/disable use of DMA transfers
- i2c: reset the I2C peripheral if there was an error on the bus
- rename mp_hal_pin_set_af to _config_alt, to simplify alt config
- upgrade to STM32CubeF4 v1.13.0 - CMSIS/Device 2.5.1
- upgrade to STM32CubeF4 v1.13.0 - HAL v1.5.1
- apply STM32CubeF4 v1.13.1 patch - upgrade HAL driver to v1.5.2
- hal/i2c: reapply HAL commit ea040a4 for f4
- hal/sd: reapply HAL commit 1d7fb82 for f4
- hal: reapply HAL commit 9db719b for f4
- hal/rcc: reapply HAL commit c568a2b for f4
- hal/sd: reapply HAL commit 09de030 for f4
- boards: configure all F4 boards to work with new HAL
- make-stmconst.py: fix regex's to work with current CMSIS
- i2c: handle I2C IRQs
- dma: precalculate register base and bitshift on handle init
- dma: mark DMA sate as READY even if HAL_DMA_Init is skipped
- can: clear FIFO flags in IRQ handler
- i2c: provide custom IRQ handlers
- hal: do not include <stdio.h> in HAL headers
- mphalport.h: use single GPIOx->BSRR register
- make-stmconst.py: add support for files with invalid utf8 bytes
- update HALCOMMITS due to change to hal
- make-stmconst.py: restore Python 2 compatibility
- update HALCOMMITS due to change to hal
- moduselect: move to extmod/ for reuse by other ports
- i2c: use the HAL's I2C IRQ handler for F7 and L4 MCUs
- updates to get F411 MCUs compiling with latest ST HAL
- i2c: remove use of legacy I2C_NOSTRETCH_DISABLED option
- add beginnings of port-specific machine.I2C implementation
- i2c: add support for I2C4 hardware block on F7 MCUs
- i2c: expose the pyb_i2c_obj_t struct and some relevant functions
- machine_i2c: provide HW implementation of I2C peripherals for F4
- add support for flash storage on STM32F415
- add back GPIO_BSRRL and GPIO_BSRRH constants to stm module
- add OpenOCD configuration for STM32L4
- add address parameters to openocd config files
- adc: add "mask" selection parameter to pyb.ADCAll constructor
- adc: provide more accurate measure of VBAT and VREFINT
- adc: make ADCAll.read_core_temp return accurate float value
- adc: add ADCAll.read_vref method, returning "3.3v" value
- adc: add support for F767 MCU
- adc: make channel "16" always map to the temperature sensor
- sdcard: clean/invalidate cache before DMA transfers with SD card
- moduos: implement POSIX behaviour of rename, allow to overwrite
- adc: use constants from new HAL version
- refactor UART configuration to use pin objects
- uart: add support for UART7 and UART8 on F7 MCUs
- uart: add check that UART id is valid for the given board
- cmsis: update STM32F7 CMSIS device include files to V1.1.2
- hal: update ST32CubeF7 HAL files to V1.1.2
- port of f4 hal commit c568a2b to updated f7 hal
- port of f4 hal commit 09de030 to updated f7 hal
- port of f4 hal commit 1d7fb82 to updated f7 hal
- declare and initialise PrescTables for F7 MCUs
- boards/STM32F7DISC: define LSE_STARTUP_TIMEOUT
- hal: update HALCOMMITS due to change in f7 hal files
- refactor to use extmod implementation of software SPI class
- cmsis: add CMSIS file stm32f767xx.h, V1.1.2
- add NUCLEO_F767ZI board, with openocd config for stm32f7
- cmsis: add CMSIS file stm32f769xx.h, V1.1.2
- add STM32F769DISC board files
- move PY_SYS_PLATFORM config from board to general config file
- mpconfigport: add weak-module links for io, collections, random
- rename mp_const_vcp_interrupt to mp_kbd_exception
- usb: always use the mp_kbd_exception object for VCP interrupt
- use core-provided keyboard exception object
- led: properly initialise timer handle to zero before using it
- mphalport.h: explicitly use HAL's GPIO constants for pull modes
- usrsw: use mp_hal_pin_config function instead of HAL_GPIO_Init
- led: use mp_hal_pin_config function instead of HAL_GPIO_Init
- sdcard: use mp_hal_pin_config function instead of HAL_GPIO_Init
- add support for STM32 Nucleo64 L476RG
- uart: provide a custom function to transmit over UART
- uart: increase inter-character timeout by 1ms
- enable utimeq module

cc3200 port:
- tools/smoke.py: change readall() to read()
- pybspi: remove static mode=SPI.MASTER parameter for latest HW API
- mods/pybspi: remove SPI.MASTER constant, it's no longer needed
- update for moduselect moved to extmod/
- re-add support for UART REPL (MICROPY_STDIO_UART setting)
- enable UART REPL by default
- README: (re)add information about accessing REPL on serial
- make: rename "deploy" target to "deploy-ota"
- add targets to erase flash, deploy firmware using cc3200tool
- README: reorganize and update to the current state of affairs
- modwlan: add network.WLAN.print_ver() diagnostic function

esp8266 port:
- enable uselect module
- move websocket_helper.py from scripts to modules for frozen BC
- refactor to use extmod implementation of software SPI class
- mpconfigport_512k: disable framebuf module for 512k build
- enable native emitter for Xtensa arch
- enable inline Xtensa assembler
- add "ota" target to produce firmware binary for use with yaota8266
- use core-provided keyboard exception object
- add "erase" target to Makefile, to erase entire flash
- when doing GC be sure to trace the memory holding native code
- modesp: flash_user_start(): support configuration with yaota8266
- force relinking OTA firmware image if built after normal one
- scripts/inisetup: dump FS starting sector/size on error
- Makefile: produce OTA firmware as firmware-ota.bin
- modesp: make check_fw() work with OTA firmware
- enable utimeq module
- Makefile: put firmware-ota.bin in build/, for consistency
- modules/flashbdev: add RESERVED_SECS before the filesystem
- modules/flashbdev: remove code to patch bootloader flash size
- modules/flashbdev: remove now-unused function set_bl_flash_size
- modules/flashbdev: change RESERVED_SECS to 0

zephyr port:
- add .gitignore to ignore Zephyr's "outdir" directory
- zephyr_getchar: update to Zephyr 1.6 unified kernel API
- switch to Zephyr 1.6 unified kernel API
- support raw REPL
- implement soft reset feature
- main: initialize sys.path and sys.argv
- use core-provided keyboard exception object
- uart_core: access console UART directly instead of printk() hack
- enable slice subscription

docs:
- remove references to readall() and update stream read() docs
- library/index: elaborate on u-modules
- library/machine.I2C: refine definitions of I2C methods
- library/pyb.Accel: add hardware note about pins used by accel
- library/pyb.UART: added clarification about timeouts
- library/pyb.UART: moved writechar doc to sit with other writes
- esp8266/tutorial: update intro to add Getting the firmware section
- library/machine.I2C: fix I2C constructor docs to match impl
- esp8266/tutorial: close socket after reading page content
- esp8266/general: add "Scarcity of runtime resources" section
- library/esp: document esp.set_native_code_location() function
- library/esp: remove para and add further warning about flash
- usocket: clarify that socket timeout raises OSError exception

travis:
- build STM32 F7 and L4 boards under Travis CI
- include persistent bytecode with floats in coverage tests

examples:
- hwapi: button_led: Add GPIO pin read example
- hwapi: add soft_pwm example converted to uasyncio
- http_client: use read() instead of readall()
- hwapi: add uasyncio example of fading 2 LEDs in parallel
- hwapi: add example for machine.time_pulse_us()
- hwapi: add hwconfig for console tracing of LED operations
- accellog.py: change 1: to /sd/, and update comment about FS
- hwapi/hwconfig_console: don't alloc memory in value()

ESP8266 port uses SDK 2.0, has more heap, has support for 512k devices

This release brings some code size reductions to the core as well as
more tests and improved coverage which is now at 94.3%.

The time.ticks_diff(a, b) function has changed: the order of the arguments
has been swapped so that it behaves like "a - b", and it can now return a
negative number if "a" came before "b" (modulo the period of the ticks
functions).

For the ESP8266 port the Espressif SDK has been updated to 2.0.0, the
heap has been increased from 28k to 36k, and there is support for 512k
devices via "make 512k".  upip is included by default as frozen bytecode.
The network module now allows access-point reconnection without WiFi
credentials, and exposes configuration for the station DHCP hostname.  The
DS18B20 driver now handles negative temperatures, and NeoPixel and APA102
drivers handle 4 bytes-per-pixel LEDs.

For the CC3200 port there is now support for loading of precompiled .mpy
files and threading now works properly with interrupts.

A detailed list of changes follows.

py core:
- py.mk: automatically add frozen.c to source list if FROZEN_DIR is defined
- be more specific with MP_DECLARE_CONST_FUN_OBJ macros
- specialise builtin funcs to use separate type for fixed arg count
- {modbuiltins,obj}: use MP_PYTHON_PRINTER where possible
- modbuiltins: add builtin "slice", pointing to existing slice type
- add "delattr" builtin, conditional on MICROPY_CPYTHON_COMPAT
- sequence: fix reverse slicing of lists
- fix null pointer dereference in mpz.c, fix missing va_end in warning.c
- remove asserts that are always true in emitbc.c
- fix wrong assumption that m_renew will not move if shrinking
- change config default so m_malloc0 uses memset if GC not enabled
- add MICROPY_FLOAT_CONST macro for defining float constants
- move frozen bytecode Makefile rules from ports to common mk files
- strip leading dirs from frozen mpy files, so any path can be used

extmod:
- vfs_fat_file: check fatfs f_sync() and f_close() returns for errors
- vfs_fat_file: make file.close() a no-op if file already closed
- utime_mphal: ticks_diff(): switch arg order, return signed value
- utime_mphal: add MP_THREAD_GIL_EXIT/ENTER warppers for sleep functions
- utime_mphal: implement ticks_add(), add to all maintained ports
- utime_mphal: allow ticks functions period be configurable by a port

lib:
- utils/pyhelp.c: use mp_printf() instead of printf()
- utils/pyexec: add mp_hal_set_interrupt_char() prototype
- libm: move Thumb-specific sqrtf function to separate file

drivers:
- add "from micropython import const" when const is used

tools:
- upgrade upip to 1.1.4: fix error on unix when installing to non-existing
  absolute path
- pip-micropython: remove deprecated wrapper tool
- check_code_size.sh: code size validation script for CI
- replace upip tarball with just source file, to make its inclusion as
  frozen modules in multiple ports less magic

tests:
- extmod/vfs_fat: improve VFS test coverage
- basics/builtin_slice: add test for "slice" builtin name
- basics: add test for builtin "delattr"
- extmod/vfs_fat_fsusermount: improve fsusermount test coverage
- extmod/vfs_fat_oldproto: test old block device protocol
- basics/gc1: garbage collector threshold() coverage
- extmod/uhashlib_sha1: coverage for SHA1 algorithm
- extmod/uhashlib_sha256: rename sha256.py test
- btree1: fix out of memory error running on esp8266
- extmod/ticks_diff: test for new semantics of ticks_diff()
- extmod/framebuf1: test framebuffer pixel clear, and text function

minimal port:
- Makefile: split rule for firmware.bin generation

unix port:
- Makefile: remove references to deprecated pip-micropython
- modtime: use ticks_diff() implementation from extmod/utime_mphal.c
- mphalport.h: add warning of mp_hal_delay_ms() implementation
- modtime: switch ticks/sleep_ms/us() to utime_mphal
- fix symbol references for x86 Mac
- replace upip tarball with just source file

windows port:
- enable utime_mphal following unix, define mp_hal_ticks_*
- fix utime_mphal compilation for msvc
- implement mp_hal_ticks_cpu in terms of QueryPerformanceCounter

qemu-arm port:
- exclude ticks_diff test for qemu-arm port
- exclude extmod/vfs_fat_fileio.py test
- exclude new vfs_fat tests
- enable software floating point support, and float tests

stmhal port:
- modutime: refactor to use extmod's version of ticks_cpu
- refactor pin usage to use mp_hal_pin API
- led: refactor LED to use mp_hal_pin_output() init function
- Makefile: use standard rules for frozen module generation
- modutime: consistently convert to MP_ROM_QSTR/MP_ROM_PTR
- enable SD power save (disable CLK on idle)

cc3200 port:
- use mp_raise_XXX helper functions to reduce code size
- mods/pybspi: allow "write" arg of read/readinto to be positional
- enable loading of precompiled .mpy files
- fix thread mutex's so threading works with interrupts

teensy port:
- update to provide new mp_hal_pin_XXX functions following stmhal

esp8266 port:
- Makefile: use latest esptool.py flash size auto-detection
- esp_init_data: auto-initialize system params with vendor SDK 2.0.0
- esp8266.ld: move help.o to iROM
- esp8266.ld: move modmachine.o to iROM
- esp8266.ld: move main.o to iROM
- add MP_FASTCODE modifier to put a function to iRAM
- main: mark nlr_jump_fail() as MP_FASTCODE
- modules/webrepl: enforce only one concurrent WebREPL connection
- etshal.h: add few more ESP8266 vendor lib prototypes
- modesp: add flash_user_start() function
- add support for building firmware version for 512K modules
- scripts: make neopixel/apa102 handle 4bpp LEDs with common code
- modutime: consistently convert to MP_ROM_QSTR/MP_ROM_PTR
- modnetwork: config(): fix copy-paste error in setting "mac"
- scripts/port_diag: add descriptions for esf_buf types
- modnetwork.c: allows AP reconnection without WiFi credentials
- main: bump heap size to 36K
- etshal.h: add prototypes for SPIRead/SPIWrite/SPIEraseSector
- etshal.h: adjust size of MD5_CTX structure
- modules: fix negative temperature in ds18x20 driver
- rename "machine" module implementation to use contemporary naming
- rework webrepl_setup to run over wired REPL
- espneopixel.c: solve glitching LED issues with cpu at 80MHz
- include upip as a standard frozen bytecode module
- update docs for esptool 1.2.1/SDK 2.0 (--flash_size=detect)
- modnetwork.c: expose configuration for station DHCP hostname

zephyr port:
- implement utime module
- use board/SoC values for startup banner based on Zephyr config
- initial implementation of machine.Pin
- zephyr_getchar: update for recent Zephyr refactor of console hooks
- support time -> utime module "weaklink"
- README: update for the current featureset, add more info
- mpconfigport.h: move less important params to the bottom
- Makefile: allow to adjust heap size from make command line
- Makefile: update comments to the current state of affairs
- Makefile: allow to override Zephyr config from make command line
- Makefile: add minimal port
- Makefile: add -fomit-frame-pointer to reduce code size
- mphalport.h: update for new "unified" kernal API (sleep functions)

docs:
- machine.SPI: bring up to date with Hardware API, make vendor-neutral
- machine.SPI: improve descriptions of xfer methods
- library/builtins: add docs for delattr and slice
- library/network: reword intro paragraph
- library/network: typo fixes, consistent acronym capitalization
- library/index: update TOCs so builtins sorted before modules
- utime: document ticks_cpu() in more detail
- utime: describe new semantics of ticks_diff() (signed ring arithmetics)
- utime: add docs for ticks_add(), improvements for other ticks_*()
- esp8266: update for new WebREPL setup procedure
- */quickref.rst: use new semantics of ticks_diff()
- library/machine.Pin: update Pin docs to align with new HW API

travis:
- integrate tools/check_code_size.sh
- minimal: Use CROSS=1, for binary size check

examples:
- http_server_simplistic: add "not suitable for real use" note
- hwapi: example showing best practices for HW API usage in apps
- hwapi: add hwconfig for DragonBoard 410c

New port to Zephyr, upip runs on baremetal, and reduction in code size

This release adds a new port of MicroPython to run on top of the Zephyr
real-time operating system.  As part of this there is now basic support for
using mbedTLS as the ussl module.  The release also brings initial support
for running the package manager upip on baremetal systems with low heap
memory (such as esp8266), through a Python module interface.

Work has been done in this release to clean up the core, removing redundant
and/or unreachable code, and factoring existing duplicated code patterns.
This brings a reduction of 828 bytes in code size to the bare-arm port, and
1368 bytes to the minimal port.  There is also improved coverage through
the addition of new tests for corner cases.

The "micropython" module sees the addition of the "const" identity function
which should be used as "from micropython import const" in scripts that
want to use the MicroPython constant optimisations in the compile stage.
There is also the addition of the "opt_level" function to change the
parser/compiler optimisation level at runtime.

The behaviour of "sys.exit" (and "raise SystemExit") on baremetal is now
changed: this function no longer does a soft-reset of the board, rather it
just stops the running script and drops to the REPL.  In order to do an
actual soft reset the "machine.soft_reset" function has been added (to the
stmhal port only, for the time being).

Following CPython, KeyError exceptions for dictionary lookups now have the
failed key stored as the argument of the exception instance, accessible as
exc.args[0].  The "ujson.load" function has also been added, to load JSON
data from an arbitrary stream.

The I2C support in the machine module now has clock stretching, the
addition of the "addrsize" parameter in memory transfer methods, and I2C
scanning now uses dummy writes instead of dummy reads to make the scanning
more reliable.

The CMSIS library has been upgrade to v4.30, and the boards section of
the stmhal port has been refactored to use a common.ld script.  The stmhal
port now has a full implementation of the machine.SPI class, with support
for both hardware SPI peripherals and fast software SPI.  The USB HID
driver in stmhal has added support to receive USB HID messages from the
host.

py core:
- asmthumb: flush D-cache, and invalidate I-cache on STM32F7
- makeqstrdefs.py: use python 2.6 syntax for set creation
- objnone: remove unnecessary handling of MP_UNARY_OP_BOOL
- move frozen modules rules from esp8266 port for reuse across ports
- combine 3 comprehension emit functions (list/dict/set) into 1
- combine 3 comprehension opcodes (list/dict/set) into 1
- vstr: remove vstr.had_error flag and inline basic vstr functions
- objnone: use mp_generic_unary_op instead of custom one
- showbc: make printf's go to the platform print stream
- remove 'name' member from mp_obj_module_t struct
- builtinimport: fix nanbox build after change to better handle -m modules
- stream: remove unnecessary check for NULL return from vstr_extend
- py.mk: suppress some compiler warnings when building berkeley-db
- shrink mp_arg_t struct by using reduced-size integer members
- update opcode format table because 3 opcodes were removed, 1 added
- parse: only replace constants that are standalone identifiers
- py.mk: add support for building modussl_mbedtls
- only store the exception instance on Py stack in bytecode try block
- vm: use MP_OBJ_FROM_PTR to cast a type to an object
- modmicropython: add micropython.const, alias for identity function
- objstr: remove unreachable function used only for terse error msgs
- emitbc: remove/refactor unreachable code, to improve coverage
- objfun: remove unnecessary check for viper fun with 5 or more args
- objfun: use if instead of switch to check return value of VM execute
- objset: use mp_check_self() to check args of set/frozenset methods
- objset: ensure that use of frozenset.update raises an exception
- compile: fix async-for/async-with to work with simpler exc on stack
- scope: use lookup-table to determine a scope's simple name
- scope: shrink scope_t struct by 1 machine word
- scope: factor common code to find locals and close over them
- compile: fix typo when checking for parse-node kind
- argcheck: simplify if-chain so that the last one is the default
- objbool: defer bool's unary op implementation to small int
- objbool: make a slight simplification of bool constructor
- modstruct: remove unreachable code, and add comment about CPy diff
- add mp_raise_OSError(errno) helper function
- objstringio: add readinto() method
- modmicropython: add micropython.opt_level([value]) function
- compile: remove unreachable code
- mpz: in divmod, replace check for rhs!=0 with assert
- mpz: use assert to verify mpz does not have a fixed digit buffer
- factor duplicated function to calculate size of formatted int
- objint: use size_t for arguments that measure bytes/sizes
- compile: remove debugging code for compiler dispatch
- lexer: remove unnecessary code, and unreachable code
- vstr: combine vstr_new_size with vstr_new since they are rarely used
- objdict: fix optimisation for allocating result in fromkeys
- objdict: actually provide the key that failed in KeyError exception
- use mp_raise_msg helper function where appropriate
- add the module specified by -m to sys.modules as '__main__'

extmod:
- modussl_mbedtls: initial implementation of mbedTLS ussl module
- uctypes: allow full 32-bit address range
- modubinascii: fix crc32() function on 32-bit platforms
- modussl_mbedtls: implement key= and cert= args to wrap_socket()
- modussl_mbedtls: use 2-component include paths
- machine_i2c: add clock stretching support
- modussl_mbedtls: add server_hostname param for wrap_socket()
- uzlib: add tinfgzip.c (gzip header parsing) from upstream
- moduzlib: DecompIO: Add support for gzip-formatted streams
- uzlib/: update uzlib to v2.0.3
- vfs_fat: add fat_vfs_statvfs(), reused from stmhal
- machine_i2c: add support for the addrsize parameter in mem xfers
- machine_spi: simplify SPI xfer function to only take one buf len
- machine_spi: factor out software SPI code from esp8266 to extmod
- machine_spi: use delay_half, not baudrate, for internal timing
- machine_spi: add optional support for fast software SPI
- vfs_fat: use mp_raise_OSError helper function
- modlwip: use mp_raise_OSError helper function
- use mp_raise_OSError helper function
- vfs_fat_file: use MP_Exxx errno constants
- uzlib: update to upstream v2.1
- machine_i2c: use writes not reads in i2c.scan()
- vfs_fat: add file and directory checks for remove and rmdir
- modujson: implement ujson.load() to load JSON from a stream
- modujson: fix nanbox build
- utime_mphal: factor out implementations in terms of mp_hal_* for reuse
- utime_mphal: sleep_us/ms(): Don't wait on negative argument
- modussl_mbedtls: add dummy setblocking() method

lib:
- interrupt_char: factor out typical Ctrl+C handling from esp8266 port
- cmsis: move CMSIS headers to lib/
- cmsis: remove CMSIS-DSP headers, they are unused
- cmsis: upgrade CMSIS-CORE to V4.30
- utils/pyexec: don't treat SystemExit as "forced exit"
- utils/pyexec: allow behaviour of SystemExit to be configurable

drivers:
- dht: use mp_raise_OSError helper function

tools:
- update upip to 0.8, fixes IPv6 support
- upgrade upip to 1.0, fully self-hosted release (without fallbacks), and
  uses stream gzip decompression (step towards support for limited-heap
  baremetal systems)
- upgrade upip to 1.1.3, initial support for running on a baremetal,
  low-heap systems (like esp8266), using Python module interface

tests:
- pyb: add test for ExtInt when doing swint while disabled
- pyb: update exp file for previously updated extint test
- extmod/urandom: add urandom tests for error cases
- basics: add errno1 test, to check basics of uerrno module
- extmod: add test for machine.time_pulse_us()
- struct1: test "l" specifier to improve coverage
- array1: add tests for "l", "L" array types to improve coverage
- get cmdline verbose tests running again
- run-tests: add --via-mpy option to run test from precompiled code
- uzlib_decompio_gz: test for DecompIO with gzip bitstream
- basics: add test case for overflowing Py stack in try-finally
- micropython: add tests for const names being replaced in parser
- cmdline/cmd_showbc: fix test now that 1 value is stored on stack
- extmod/vfs_fat_ramdisk: add test for VFS.statvfs()
- float: add test for parsing a float from an empty string
- basics: add test for set.difference_update with arg being itself
- basics: add further tests for nonlocal scoping and closures
- import: add test for compiling "import a.b as c"
- basics: add test constructing a set from a non-trivial expression
- basics: add test for printing OSError when errno is unknown
- run-tests: disable cmdline/cmd_showbc test on Windows
- extmod/btree1: checks for put, seq, string print and unsupported binary op
- fix expected output of verbose cmdline test
- extmod/uzlib: test adaptive huffman tree for tinflate coverage
- improve coverage of struct with test for non-compliant behaviour
- io/write_ext: add description comment
- io/bytesio_ext: add test for readinto()
- micropython: add test for micropython.opt_level() function
- improve test coverage of py/compile.c
- extmod/vfs_fat: test coverage for remove() and rmdir()
- extmod: add test for ujson.load()
- extmod/vfs_fat: replace asserts with prints and expected outputs
- micropython: add tests for heap_lock, and emergency exceptions
- cmdline: improve coverage test for printing bytecode
- improve coverage of array, range, dict, slice, exc, unicode
- add test to print full KeyError exc from failed dict lookup
- run-tests: enable extmod/machine1.py on pyboard

unix port:
- fix build for when MICROPY_PY_SOCKET=0
- modjni: implement subscription for object arrays
- modjni: add array() top-level function to create Java array
- modjni: array(): Support creation of object arrays
- enable btree module for coverage build
- use mp_raise_OSError helper function
- use common RAISE_ERRNO macro from mphalport.h

windows port:
- enable MICROPY_PY_UERRNO

qemu-arm port:
- enable lots of extmods and enable tests for them

stmhal port:
- lcd: de-assert chip select after completing SPI transmission
- {accel,lcd}: use GPIO_{set,clear}_pin
- extint: force 0 to 1 transition on swint()
- boards: add pllvalues.py script to compute PLL values for sysclk
- boards: for OLIMEX_E407, enable UART1 and fix I2C1 mapping
- use attribute to avoid inlining
- put common definitions from linker files to common.ld
- remove STM32CubeF2 HAL files, they are unused/unsupported
- modmachine: fix clearing of reset-cause flags
- add virtual com port support for STM32L476DISC
- remove CMSIS STM32F2xx files, they are unused/unsupported
- spi: simplify spi_transfer function to take only one buf len arg
- mphalport: implement mp_hal_pin_{input,output,write}
- spi: make machine.SPI class conform to correct API
- mphalport: fix mp_hal_pin_write to use correct pin_mask
- spi: use software SPI if no periph id given, even if pins given
- spi: enable use of fast software SPI
- fix linker map for STM32L476 chips
- usbdev: add OUT endpoint to HID interface
- usb: add support to receive USB HID messages from host
- usb: use correct ClassData structure for HID receive
- usb: use real packet size (not maximum) in HID receive
- fix ESPRUINO_PICO by adding ld scripts with correct flash size
- mphalport: change pin obj type to const pointer, to avoid casts
- moduos: implement total-number-of-blocks field in statvfs
- disable network and usocket for ESPRUINO_PICO
- enable machine.time_pulse_us() function
- use mp_raise_OSError helper function
- pybstdio: use size_t instead of mp_uint_t
- modutime: refactor to use extmod/utime_mphal.c
- implement machine.soft_reset()
- enable str.center(), str.[r]partition() and builtin compile()

cc3200 port:
- add ssl_version argument to ssl.wrap_socket()

esp8266 port:
- Makefile: rename SCRIPTDIR to FROZEN_DIR for consistency with FROZEN_MPY_DIR
- ets_alt_task: ets_post: Should return 0 on success, !0 - failure
- esp_mphal: add tentative change to mp_hal_stdin_rx_chr() to wait IRQ
- extend system microsecond counter to 64-bits; use in ticks_ms
- add uos.statvfs() to get filesystem status
- moduos: move stat/statvfs funcs to sit within #if VFS guard
- modmachine: idle(): Return number of CPU cycles spent idling
- main: put /lib before / in sys.path
- modpybrtc.c: implement machine.RTC.alarm_left()
- make PY_UHASHLIB_SHA1 config depend on PY_USSL and SSL_AXTLS
- add FLASH_MODE,FLASH_SIZE options for make deploy target
- use mp_raise_OSError helper function
- make neopixel support configurable
- mpconfigport: enable MICROPY_PY_BUILTINS_SLICE_ATTRS
- enable sys.{stdin,stdout,stderr}.buffer for raw serial access
- enable importing of precompiled .mpy files
- enable micropython.alloc_emergency_exception_buf()

zephyr port:
- initial Zephyr RTOS port, MicroPython part
- initial Zephyr RTOS port, Zephyr part
- add zephyr_getchar module to handle console input
- switch to microkernel, required for network to work in background
- automatically derive ARCH
- support extra make targets
- Makefile: automatically derive target-specific CFLAGS
- use recently added "make outputexports" Zephyr target
- add README
- enable stack checking and micropython.mem_info()
- enable frozen modules support
- main: execute main.py frozen module on boot, if available
- zephyr_getchar: add support for Ctrl+C handling
- add Ctrl+C handling
- implement the help() function
- add copyright blurbs

README:
- remove issue-stats badges, the service is no longer available
- mention _thread module availability in select ports

docs:
- library/pyb.SPI: init(): describe "bits" argument
- library/machine: update description of disable/enable IRQ funcs
- uos: add uos.statvfs() documentation
- wipy: correct deep sleep current figure
- wipy: small doc fixes
- reference: add constrained.rst doc

travis:
- abandon mingw32 in favour of mingw-w64
- run feature and coverage test for precompiled mpy files

examples:
- network/http_client*: use \r\n line-endings in request

Support for stream decompression in uzlib, and more ESP8266 features

This release includes some bug fixes, code clean-up, updates to the docs,
more tests, and various feature additions.  The uzlib module now supports
efficient stream decompression in the form of the uzlib.DecompIO class.
Freezing of bytecode now supports floats for the ESP8266 port, as well as
complex numbers for all ports.  The stmhal port has ADC working on L4
microcontrollers, fixed initialisation for DAC, and addition of the
machine.WDT class and machine.reset_cause function.

For the ESP8266 port Pin(16) now works as an input pin and the hardware
SPI peripheral is exposed as machine.SPI(1).  The os.umount function is
implemented and the port supports mounting of externally connected SD
cards.  The machine.WDT class is added, wlan.scan() is fixed to return all
access points, and there is support for DS18S20 devices.

py core:
- runtime: factor out exception raising helpers
- runtime: define mp_check_self(pred) helper macro
- objdict: get rid of asserts (remove/replace with mp_check_self())
- get rid of assert() in method argument checking functions
- objtuple: in tuple_cmp_helper, use mp_check_self instead of raising
- objstr: use mp_raise_{Type,Value}Error instead of mp_raise_msg
- obj.h: for obj reprs A,B,C use void* explicitly for mp_obj_t typedef
- mpconfigport.h: remove typedef of machine_ptr_t, it's no longer needed
- sequence: allow to use bignums as indices in slice objects
- stream.c: use mp_obj_get_type in mp_get_stream_raise
- gc: add MICROPY_GC_CONSERVATIVE_CLEAR option to always zero memory
- compile: don't compile assert statements when optimisations enabled
- modstruct: use more compact mp_raise_ValueError function
- emitglue: use more compact mp_raise_ValueError function
- rename struct mp_code_state to mp_code_state_t
- mkrules.mk: allow to override name of libmicropython.a
- mpprint: fail an assertion with unsupported format specifiers
- makeqstrdata.py: compute the qstr hash from bytes, not characters
- if str/bytes hash is 0 then explicitly compute it
- emitglue.c: provide mp_raw_code_load_file for any unix architecture
- add MICROPY_USE_INTERNAL_PRINTF option, defaults to enabled

extmod:
- modwebrepl: set_password(): raise exception for too long password
- uzlib/: update uzlib to v2.0: new API supporting stream decompression
- moduzlib: refactor to new stream-compatible uzlib 2.0 API
- uzlib/: update uzlib to v2.0.1: fixes for pedantic compiler warnings
- uzlib/: update uzlib to v2.0.2: consistently use stdint types
- modbtree: do CHECK_ERROR after __bt_seq()
- modubinascii: implement binascii.crc32
- modubinascii: make crc32() support configurable
- modframebuf: fix pixel accessor to return a 1-bit result
- add machine_spi with generic SPI C-protocol and helper methods
- modframebuf: fix fill and scroll when height not divisible by 8
- moduzlib: implement zlib stream decompressor class, DecompIO
- moduzlib: use mperrno.h for error constants
- modframebuf: include font from stmhal directory explicitly
- moduzlib: support wbits arg to DecompIO
- framebuf: add the xstep!=0 case to scroll() method

lib:
- utils/stdout_helpers: fix function signature to match py/mphal.h
- berkeley-db-1.xx: update to upstream, fixes MacOSX build
- utils/pyexec: qstr_pool_info() requires size_t* parameters

drivers:
- sdcard: port the SDCard driver to new machine API, with backwards
  compatibility for pyboard

tools:
- mpy-tool.py: support freezing float literals with obj-repr C
- mpy-tool.py: store qstr config values in global config object
- mpy-tool.py: compute the hash value for str/bytes objects
- mpy-tool.py: support freezing of complex numbers

tests:
- rename zlibd_decompress.py -> uzlib_decompress.py
- basics: add more tuple tests to improve coverage testing
- basics: add more list tests to improve coverage testing
- misc/non_compliant: add tests to improve coverage testing
- basics: add test for break from within try within a for-loop
- basics: add a test file for overriding special methods
- basics/special_methods: enable tests for extra special methods
- uzlib_decompress: actually test raw DEFLATE stream
- run-tests: disable thread/thread_lock4.py on Travis
- run-tests: disable thread/stress_heap.py when running on Travis
- cmdline: add test for -O option to check optimisation value
- extmod/vfs_fat_ramdisk: add tests for VFS.umount()
- run-tests: disable thread_gc1.py test on Travis
- unix/extra_coverage: add test for str/bytes with invalid hash
- extmod: add test for uzlib.DecompIO
- extmod: add a test for framebuf module, tested by coverage build
- extmod/uzlib_decompio: add zlib bitstream testcases
- extmod/framebuf1: add tests for scrolling in the x-direction
- run-tests: disable thread/stress_recurse.py test on Travis

unix port:
- mpconfigport.h: don't include stdio.h on MacOS
- when find'ing frozen files don't use extra slash, do follow symlinks

qemu-arm port:
- enable MICROPY_PY_ALL_SPECIAL_METHODS

stmhal port:
- boards: update STM32L476 pin defs to include ADC channels
- adc.c: get ADC working on STM32L4 MCUs
- fix timer capture/compare interrupt handling for TIM1 and TIM8
- remove obsolete code for special handling of TIM3 irq settings
- make ADC channel 16 available on L4 MCUs
- update pin print to print new constants
- modusocket: set self->nic to MP_OBJ_NULL after socket close
- update boot.py files to use VCP instead of CDC
- spi: factor out SPI transfer code to a single function
- spi: support new machine SPI methods in legacy SPI object
- add machine.WDT class
- set STM32F7DISC CPU Frequency to 216 MHz
- dac: fix DAC (re-)initialisation by resetting DMA
- wdt: implement keyword args to WDT constructor
- modmachine: implement machine.reset_cause() function, and consts
- machine.POWER_ON is renamed to machine.PWRON_RESET
- when find'ing frozen files don't use extra slash, do follow symlinks

cc3200 port:
- add machine.PWRON_RESET constant (machine.POWER_ON is now deprecated)

teensy port:
- fix execution of frozen boot.py and main.py

esp8266 port:
- fix reading of pin object for GPIO16; Pin(16) now works as an input
- PULL_UP is not supported on Pin(16), so raise an exception in this case
- enable support for all special methods
- modpybhspi: add a HSPI module for hardware SPI support
- modmachinespi: add a factory method for SoftSPI/HSPI
- esp_mphal: no longer disable watchdog on startup
- modpybrtc: use 64-bit arithmetic when computing alarm expiry
- hspi: enable duplex operation of hardware SPI
- modous: add os.umount method to unmount a filesystem
- modmachinewdt: implement machine.WDT class
- modules: split onewire.py into OneWire and DS18X20 driver
- modules/onewire: change onewire.read() to onewire.readinto()
- modules/ds18x20.py: add support for DS18S20 devices
- modpybspi: use generic SPI helper methods to implement SPI
- modpybhspi: simplify HSPI driver by using 1 function for xfers
- modmachinewdt: add .deinit() method
- modmachine: add WDT_RESET and SOFT_RESET constants
- modmachine: don't expose internal SoftSPI and HSPI classes
- modmachine: simplify SPI class implementation multiplexing
- espneopixel: disable IRQs during eps.neopixel_write
- modnetwork: fix wlan.scan() method so it returns all networks
- modmachine: map PWR_ON_RESET to vendor's REASON_DEFAULT_RST
- machine.PWR_ON_RESET is renamed to machine.PWRON_RESET
- when find'ing frozen files don't use extra slash, do follow symlinks

docs:
- esp8266/tutorial/pins: fix typo in commands for pin input mode
- esp8266/intro: add command to install esptool.py 1.0.1 via pip
- library/machine.WDT: add note that WDT is only available on WiPy
- esp8266/quickref: fix and update the SPI docs
- esp8266: update quickref and tutorial for OneWire/DS18X20 driver
- pyboard: update USB mouse tutorial to use VCP instead of CDC
- pyboard: update USB mouse tutorial to use pyb.USB_HID()
- library: add reference for pyb.usb_mode and pyb.USB_HID
- pyboard/quickref: add links to pinouts for other pyboard variants
- pyboard/quickref: add section on "delay and timing" for utime mod
- esp8266/quickref: add internal links to docs for some modules
- esp8266/quickref: update information on SPI classes
- esp8266/quickref: further improvements for SPI subsections
- library/machine.WDT: add that WDT is available on pyboard
- reference/isr_rules.rst: two minor additions to docs for using ISR

misc:
- add *.pyc to .gitignore, because Python 2 doesn't use __pycache__
- build mpy-cross as part of the Travis process