added partial mouse events on osx

engine/app.cpp

@@ -486,3 +486,16 @@ void App::resize(float w, float h)
     YGNodeStyleSetHeight(y_root, height);
     update_layout();
 }
+
+void App::mouse_down(int button, float x, float y)
+{
+    printf("mouse click %f %f\n", x, y);
+}
+void App::mouse_move(float x, float y)
+{
+    
+}
+void App::mouse_up(int button, float x, float y)
+{
+    
+}