change chan osc range - PLEASE READ

as of now the range is ~32768, either from -16384 to 16383, or 0 to 32767.
it previously was -32768 to 32767 (~65536).

this change was made to better suit chips that only output a positive value.
if you are working on a new chip, update your code and shift right by one if necessary.

src/engine/platform/segapcm.cpp

@@ -49,7 +49,7 @@ void DivPlatformSegaPCM::acquire(short** buf, size_t len) {
     buf[1][h]=os[1];
 
     for (int i=0; i<16; i++) {
-      oscBuf[i]->data[oscBuf[i]->needle++]=pcm.lastOut[i][0]+pcm.lastOut[i][1];
+      oscBuf[i]->data[oscBuf[i]->needle++]=(pcm.lastOut[i][0]+pcm.lastOut[i][1])>>1;
     }
   }
 }