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/dispatch.h

@@ -1,6 +1,8 @@
 #ifndef _DISPATCH_H
 #define _DISPATCH_H
 
+#define ONE_SEMITONE 2200
+
 enum DivDispatchCmds {
   DIV_CMD_NOTE_ON=0,
   DIV_CMD_NOTE_OFF,
@@ -64,7 +66,7 @@ class DivDispatch {
      * the engine shall resample to the output rate.
      */
     int rate;
-    virtual void acquire(short& l, short& r);
+    virtual void acquire(int& l, int& r);
     virtual int dispatch(DivCommand c);
     virtual void tick();