Introduce D107 code for missing __init__ docstring

Declare Python 3.6 support

- Enabled tests in ``tox.ini`` and ``.travis.yml``
- Declare support for 3.6 in ``README.rst`` and ``docs/release_notes.rst``

Fix bug where snowballstemmer chokes on Unicode word

Mark missing docstrings for nested classes as violation D106

# Conflicts:
#	docs/release_notes.rst

Some tools like prospector tried to import a v1 pydocstyle or a v2 pydocstyle and
uses them the same way, BUT there has been a breaking change introduced here and so
`ignore_decorators` must be provided. This breaks at least prospectors behavior. 

May we set just a default=None value to have the same signature for the v1 and v2 function here.

Some tools like prospector tried to import a v1 pydocstyle or a v2 pydocstyle and
uses them the same way, BUT there has been a breaking change introduced here and so
`ignore_decorators` must be provided. This breaks at least prospectors behavior. 

May we set just a default=None value to have the same signature for the v1 and v2 function here.

Added --config flag

Added matrix multiplication operator handling

Backport parser tests and some changes from Jedi branch