===== main.c =====

Lots of different functions in here:

==== do_tempo ====
This is essentially a software interupt.  A huge function with a big fat case statement in it.  Handles note playing, amongst other things.

==== Signals ====
=== Output Compare ===
Handles sync and tempo.  Deals with DinSync and Midi Sync.

=== Pin Change ===
Handles the tempo knob.

==== main ====
Handles initialization, and is the main loop of the program