code: func (f *FSM) afterEventCallbacks(e *Event) {
  	if fn, ok := f.callbacks[cKey{e.Event, callbackAfterEvent}]; ok {
  		fn(e)
  	}
  	if fn, ok := f.callbacks[cKey{"", callbackAfterEvent}]; ok {
  		fn(e)
  	}
  }
docs: // afterEventCallbacks calls the after_ callbacks, first the named then the
  // general version.