#10 Efficient fork handling

This should include handling situations where the fork is not directly linkable to the original repository via e.g. GitHub's "forked from" information, e.g. when someone forked a GitHub project onto GitLab or some other platform. On Git, a repository can be uniquely identified with the root commit's hash. However, repositories can have multiple root commits via orphan branches and even on a single branch when merging independent histories. Related: #1