Migrate to Rugged (libgit2)

[ioquatix]

A lot of the internals of teapot directly invoke the git command line which is a pretty basic way of interacting with the repositories. Using Rugged provides structured interface to git. It makes it easier to implement more advanced commands without needing to parse the output of git commands.

[ioquatix]

This is now complete. It also improved performance quite a bit for package fetching.