Audioscrobbler track.updateNowPlaying support

[ChrisW-B]

Hi, I'm using a client that seems to solely make a request to track.updateNowPlaying on the /apis/audioscrobbler/2.0/ endpoint - would you be open to a PR to add some support for that endpoint?

I'm imagining it might be simpler than Last.FM's, they presumably add some sort of hold to the play so that it gets converted to a scrobble at a certain point. Most likely maloja would instead just accept it as equivalent to a track.scrobble call.