earliest multi-chip support

no saving, no adding chips yet...
only the beginning

src/engine/engine.h

@@ -94,6 +94,8 @@ struct DivDispatchContainer {
   int cycles, clockDrift;
 
   void setRates(double gotRate);
+  void acquire(size_t offset, size_t count);
+  void fillBuf(size_t runtotal, size_t size);
   void clear();
   void init(DivSystem sys, DivEngine* eng, int chanCount, double gotRate, bool pal);
   void quit();