Merge branch 'master' of https://github.com/tildearrow/furnace into x1_010

# Conflicts:
#	CMakeLists.txt
#	papers/doc/7-systems/README.md
#	src/engine/dispatch.h
#	src/engine/dispatchContainer.cpp
#	src/engine/playback.cpp
#	src/engine/sysDef.cpp
#	src/gui/gui.cpp

src/engine/engine.cpp

@@ -858,6 +858,9 @@ void DivEngine::stop() {
   sPreview.sample=-1;
   sPreview.wave=-1;
   sPreview.pos=0;
+  for (int i=0; i<song.systemLen; i++) {
+    disCont[i].dispatch->notifyPlaybackStop();
+  }
   isBusy.unlock();
 }