added partial mouse events on osx

engine/app.hpp

@@ -26,6 +26,9 @@ public:
     void create();
     void update(float dt);
     void resize(float w, float h);
+    void mouse_down(int button, float x, float y);
+    void mouse_move(float x, float y);
+    void mouse_up(int button, float x, float y);
     void update_layout();
     void load_layout();
 };