Most protracted README update ever.

Integrate fix from behackett, and additional tests

Oops - the current release is 1.3.0, so the next one should be 1.3.1 not 1.3.2

Tests failed as expected due to the previous change, so re-apply the fix.

Also add -v to the pytest invocation to enumerate the test cases in the output.

* Assert that we leaked zero bytes in test_leaks_client.
* Rename test_leaks_server to test_leaks_server_linux, and skip this test if we're not on Linux, because the method used to check for leaked file descriptors is specific to Linux.
* Assert that test_leaks_server_linux doesn't leak any FDs
* This change includes no "guaranty's", only "guarantees"

Pip no longer likes Python3 versions less than 3.4, so remove the 3.3.6 test, and while we're here, add 3.7.0.

Here's an example of the failure seen in 3.3.6:
https://travis-ci.org/dreness/ccs-pykerberos/jobs/439460827

... and demonstrate the sort of embarrassment one might expect when making changes without the use of a local python interpreter.

Python2's xrange is Python3+'s range, while Python3's xrange isn't a thing at all.

Merge branch 'buildvalleak' of git://github.com/behackett/ccs-pykerberos into behackett-buildvalleak

Resolves #70

Adding MANIFEST.in from current 1.2.5 sdist release on PyPI

Enable Travis CI testing of python2.6

Fix gss_server_state cast

Use destructors to free client and server state

Fix building on older Pythons

This change obsoletes the functions authGSSClientClean and
authGSSServerClean. The client and server state are now
destroyed when the PyCapsule / PyCObject storing them are
reclaimed. The functions remain to avoid breaking backward
compatibility, but just return AUTH_GSS_COMPLETE.

Resolves #48.