Enhance the monophonic and polyphonic algorithms

[vincentcourtois]

Monophonic algorithm

• A first key is pressed
• The envelope is triggered as the sound starts to play
• Another key is pressed
• The note changes, but the envelope is NOT retriggered
• The new note is released
• the envelope is NOT triggered as "released" and the former note is played in place of the note released

Polyphonic algorithm

When a note is played after all the polyphony channels have been filled, this note takes the channel of the last played note for the device (last in, first out)