When defining `long_description` in setup.cfg using the `file:`
directive, we need to keep everything on one line. Otherwise, it will
treat the value as a block of literal text.

Python 3.4 has reached end-of-life so remove it from the set of
officially supported Python versions.

Since setuptools 30.3.0 we can use setup.cfg to configure package
for build and distribute. These changes propose to adopt a more
modern approach to package pymemcache by using latest and stable
feature of setuptools.

Overview:
- remove python code to maintain
- introduce package metadata,
- centralize version management in package metadata

We can no longer import the __version__ attribute because there is no an
implicit runtime dependency on six (as of #197), and we can't guarantee
that six is installed until *after* setup.py is parsed and run.

Instead, parse the `__version__ = 'x.y.z'` string from __init__.py to
extract the version.

Fixes #214

Also fix a minor flake8 issue in setup.py.