git-and-tools/hub: New package, version 1.10.3.

This is a small wrapper of Git, which integrates some GitHub specific features,
especially stuff like merging or sending pull requests or attaching commits to
an issue.

I'm not quite familiar with the Nix integration of Ruby, so let's hope that I'm
not doing something horrible here.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>