ENH: Make all Msg args but 'command' optional.
ENH: Make all Msg args but 'command' optional.

klauer/bluesky,sameera2004/bluesky,klauer/bluesky,ericdill/bluesky,sameera2004/bluesky,dchabot/bluesky,ericdill/bluesky,dchabot/bluesky