a lot of work

- round to nearest instead of round to zero in SMS period calc
- implement arpeggio
- implement arp macro (kinda)
- polish the SMS platform
- correct the DIV_CMD_PITCH range to 1 semitone
- fix PSG volume in Genesis
- use a better register write strat in Genesis
- fix a bug caused by legacy code
- implement ECxx command
- implement EDxx command
- implement SN noise mode command
- vibrato table is now 64 positions long (instead of 60)

src/engine/platform/dummy.cpp

@@ -1,7 +1,7 @@
 #include "dummy.h"
 #include <math.h>
 
-void DivPlatformDummy::acquire(short& l, short& r) {
+void DivPlatformDummy::acquire(int& l, int& r) {
   l=0;
   for (unsigned char i=0; i<chans; i++) {
     if (chan[i].active) {