// Quit elegantly exits out of the main event loop.
// "Elegantly" in this case means that it finishes processing the current
// event, and breaks out of the loop afterwards.
// There is no particular reason to use this instead of something like os.Exit
// other than you might have code to run after the main event loop exits to
// "clean up."
func Quit(xu *xgbutil.XUtil) {
xu.Quit = true
}