Digestcmd

A further refinement of the previous work on digests. This branch ports the bumpdigests.py script to MM3, and renames the send-digests CLI command to the more generic 'digests' command, which has options --bump and --send. You can use both but bump will happen before send.

This also exposes digest bump and send through the REST API. You can now POST to <api>/lists/<listid>/digest and the POST data can contain either or both of send=True and bump=True. Doing a GET on that resource returns the volume and digest numbers (read-only, just like as with the list configuration).

Also a bit of refactoring, and boosting coverage to 100% in places.