Starts playing of the specified playlist. This method acts in separate
thread and returns execution control immediately. If there is a previous
playing, initiated prior to this call, it will be silently
cancelled. You may specify the desired track number and a position in
audio file to begin playing from.
playlist - A playlist to play
startingTrackNum - A desired 0-based track number to play from
startingPosMsec - A position in audio file in milliseconds to start playing from