Only check ast.Name for their id in metaclass check

This should avoid attribute errors for checking the ``id`` attribute on
classes that don't have a basic inheritance declaration.

Closes gh-53

Also restructure to ensure we're testing the right stuff.

Move "__ in function name" check to new N807 code

Use the project's canonical PyCQA URL

This check appears controversial (#9) because PEP8 doesn't mention this
as an official naming rule. This change moves it to its own error code
so that it can be disabled separately.

Consider all metaclass methods to be class methods

It's a widely used (but perhaps not official?) convention to consider a
metaclass's methods to be class methods and to use `cls` as the first
argument (rather than `self`).

Use the simple heuristic of "class inherits from `type`" to identify
metaclasses and mark all of their methods as CLASSMETHOD.

Bump version and add release notes for 0.5.0

Add configurable list of classmethod / staticmethod decorators

- Added support for parsing CLI-style flake8-config parameters in tests
  using flake8_polyfill (has a stable API which flake8>=3 lacks)
- Removed support for multiple `codes` in testcases (unused)
- Clean up incorrect usage of default which caused redundant work in
  parse_options for ignore_names

Fixes #38

Show offending symbol as part of the  message

Fixes github issue #31

Drop Python 2.6 support

make some regexps raw strings

Correct N804/N805 for __init_subclass__

According to pep 0487, the `__init_subclass__` method is implicitly
considered a classmethod. Thus it should be considered as an exception
of N804/N805 (first argument should be named self/cls). This is already
implemented for `__new__` so extend using the same logic.

to avoid DeprecationWarnings with Python 3.6

Travis CI's pypy3 is very old and breaks when we try to use setuptools
with it. Python 3.6 is something we should start testing on.

Include license

Bump version to 0.4.0

Include tests in release source tarball

Fix failing builds on Python 3.2

A test suite is a very useful thing, it would be great to include in the
release tarball that is uploaded to pypi. That way people who download
and build the release can run the tests to ensure the library is
working.

Linux distributions, such as Debian, base their packages of Python
modules on the pypi release. This means the test suite can be run when
building a Debian package, and so catch mistakes in the packaging or
errors introduced into dependencies.

I've written some more on this topic on the Debian Python mailing list.

  https://lists.debian.org/debian-python/2016/04/msg00074.html

Fix the way ignored names are split