phabricator: add phabsend command to send a stack The `phabsend` command is intended to provide `hg email`-like experience - sending a stack, setup dependency information and do not amend existing changesets. It uses differential.createrawdiff and differential.revision.edit Conduit API to create or update a Differential Revision. Local tags like `D123` are written indicating certain changesets were sent to Phabricator. The `phabsend` command will use obsstore and tags information to decide whether to update or create Differential Revisions.