setup.py, package, .gitignore and code fixes

* add setup.py so this is pip installable
* move the script to bin/
* create djangocompatlint module
* move rules registration code from the script to djangocompatlint
  module
* add --verbose flag to make it easier to figure out if it's checking
  the files you think it's checking
* did some minor code cleanup

Fixes #3

Hope this helps!