Moving plumbum out of the bin directory.

This relies on .bashrc's PYTHONPATH setting, which could mean that .python shouldn't be a virtualenv anymore.
Moving six to follow plumbum.
Moving the git-df/git-ci shared logic into the new python path.
Splitting git-df and git-ci into their own files.
Using plumbum.cli to simplify git-ci.
Simple script to interpret command-line parameters.