MyAudioDevice: Get/set start and end times, volume

MyAudioDevice now includes methods for setting volume, start and end
times (I haven't tested these with actual times, because I don't have a
good way to change this in the program.) Method exists to change tempo,
but it does nothing yet. Also, consider using the term "speed" instead
of "tempo" because changing the tempo without changing the pitch will be
difficult without a prebuilt media player.