Most people know about pep8 which enforce coding style.  pyflakes
goes a step beyond by analyzing the code.

flake8 is basically a wrapper around both pep8 and pyflakes and comes
with some additional checks.  I find it very useful since you only
need to require one package to have a lot of code issues reported to you.

This patch provides a 'flake8' tox environement to easily install and
run the utility on the code base.  One simply has to:

     tox -eflake8

The env has been added to the default list of environement to have
flake8 run by default.

Configuration tweaking is done in setup.cfg [flake8] section.

The repository in its current state does not pass checks We can later
easily ensure there is no regression by adjusting Travis configuration
to run this env.

More informations about flake8: https://pypi.python.org/pypi/flake8

This time with support for measuring coverage.
Ability to test quickly across multiple Python versions is crucial for
working on Python 3 compatibility...

In the process, I removed tox as it made things so much more complex for me.