Tentative independence from vendored pep8

I'm fairly certain we no longer need the copy we had of pep8.
Forgot to remove pep8.py
I was wrong. Forgot a couple lines
flake8/ now passes flake8
Filter out our options before passing to pep8

Update the .hgignore with a few pet peeves.
This is what I meant to do in a03347e
Split up flake8/run.py

I've preserved the API for users expecting their hooks and other things to
work.

That said, I'm working on #51 now as well.