sustains notes in 4 ordered sets. input notes are added to the currently
active set. switch between sets using control notes specified in sliders:
set 1/2/3/4: sends note ons for notes in the set, then sends note offs for
any previous set. if the set is already active, advances to next set.
when changing sets, sustained notes are added to the new set.
stop: sends note offs for any current set.
next: advances to next set
delete notes: while sustained, notes played are removed from the active set.
delete seq: clears the current set. if there are sustained notes, they
are retained in the current set. otherwise, if the set was playing,
advances to the next set.
fwiw, this concept needs design work. a "toggle notes" mode would be nice.
still big fun though.