PEP: fix up *.pyx

[jreback]

we don't by default check the .pyx files, we should. So this issue will cover fixing & updating the setup.cfg, need to add: filename: *.py, *.pyx

[jreback]

flake8 windows.pyx --select=E501,E302,E203,E226,E111,E114,E221,E303,E128,E231,E126,E128

seems to catch whitespace things and not bork on some cython specific pep things.

am going to include a filter for this in a future PR.