code: func (app *Application) Quit() {
  	ev := &eventAppQuit{}
  	ev.SetEventNow()
  	if scr := app.screen; scr != nil {
  		go func() { scr.PostEventWait(ev) }()
  	}
  }
docs: // Quit causes the application to shutdown gracefully.  It does not wait
  // for the application to exit, but returns immediately.