Assign Phabricator reviewers based on module ownership

At Traveloka, Indonesia’s leading travel booking site, we use Phabricator for code reviews - and as a growing company it might not be straightforward to figure out who is knowledgeable about a particular part of the code base and thus would be a good reviewer. Inspired by Quora’s Moving Fast With High Code Quality post, we are thus implementing a review routing system - the code is live on GitHub at phabricator-utils.