Improve perceived responsiveness to pause/skip

[lbt]

Snapcast responds quickly to sound starting to play but, due to buffering, seems sluggish when responding to a pause/skip.

Could snapserver accept a control signal to flush the existing buffer and tell clients to do so as well.

Stream playback would resume immediately with an empty buffer (just as it does when a stream begins)

This would need additional support from clients however in the interim a helper client listening to the mpd control protocol could easily respond to such events and signal snapserver to tell the clients to perform a buffer flush.