Added docs to server's shutdown docstrings

Add distrib test utilities for c++

C# less verbose logs

Document cardinality violation status codes

PHP: remove explicit version in composer.json

Doc Fixit: Introduce C++ style guide

Proto server reflection

Fixed bug with server initial metadata type translation

PHP: add optional channel argument to BaseStub constructor

Added unit test for generic empty stream

Expand corpus, make one-shot runners not self-check leaks (to give ASAN a chance)

Fix fuzzing detected bug

Initial Python3 support

Add a doc for the command line tool

Add support for clang3.5, clang3.7 and gcc4.6  in run_tests.py

PHP: ran php-cs-fixer again

Use == instead of is for cygrpc.OperationType values

Notable Changes:
  -Convert all str types to byte types at cython layer (ascii encoding)
  -Use six for packages that have different names in Python2/Python3
  -By default, unit tests are compiled/run in Python2.7 and Python3.4
  -Ensure MACOSX_BUILD_TARGET is at least 10.7