Add py-gitdb2 2.0.0

GitDB allows you to access bare git repositories for reading and writing. It
aims at allowing full access to loose objects as well as packs with performance
and scalability in mind. It operates exclusively on streams, allowing to handle
large objects with a small memory footprint.

WWW: https://pypi.python.org/pypi/gitdb2
WWW: https://github.com/gitpython-developers/gitdb