void mav_callbackMouseSet(int but, MAV_window *w, MAV_class *c, MAV_callbackMouseFn fn);
int mav_callbackMouseExec(int but, MAV_window *w, MAV_object *o, MAV_mouseEvent *me);
When a mouse event is detected by mav_eventsCheck, and a mouse callback has been registered for that class of object, the system calls mav_callbackMouseExec to execute fn, passing it the mouse event data me.