Raw.xs: Introduce git_sv_to_commitish
Graph.xs: Added is_ancestor_od Commit.xs: Added ancestor()
Repository.xs: merge_base() now accepts a commitish
Changes: update (closes #88)
Repository.xs: Cleanup
Repository.pm: Fix typo in example
Reduce boilerplate
Diff.xs: Add find_similar()
Diff/Stats.xs: Added insertions(), deletions(), files_changed() and buffer()