add some basic playback code!

here it begins

src/engine/platform/abstract.cpp

@@ -5,10 +5,13 @@ void DivDispatch::acquire(short& l, short& r) {
   r=0;
 }
 
+void DivDispatch::tick() {
+}
+
 int DivDispatch::dispatch(DivCommand c) {
   return 1;
 }
 
 int DivDispatch::init(DivEngine* p, int channels, int sugRate) {
   return 0;
-}
+}