This patch allows Watson to sync via a simple git repository, making it
unnecessary to run a specific backend. Instead, any git repository with
write access will do.

You can configure a git backend by setting something like:

    watson config backend.repo [email protected]:user/repo.git

If y repository is set, the `sync` command will try using git. If not,
the old backend server is used if `server` and `token` are set.

To make the stats more legible, this patch uses color for the summary
lines printed out so they stand out more from the git logs.

This should minimize the changes when different clients commit to the
repository.