MAINT: add a flake8 tox env + make okonomiyaki flake8 error-free.
BUG: fix travis-ci install script.
BUG: we must enable unittest six.moves on every python version.
MAINT: fix tox file to install unittest for python < 3.
MAINT: fix travis-ci script.
STY: revert back to 79 columns.
MAINT: pypy on travis-ci needs unittest2 as well.
Merge pull request #25 from enthought/flake8

MAINT: add a flake8 tox env + make okonomiyaki flake8 error-free.