major overhaul

still buggy, but less buggy than before. also: way more interesting and
structured sequences! whoah! wow!
works best if Markov unit_size is something other than TPQ/2 or TPQ/1.
if Markov unit_size > TPQ, then the MIDI files become weird and buggy.
and not in an appealing way either. idk why. figure that out later tho.