code: func New(final func(os.Signal), notify ...func()) *Handler {
  	return &Handler{
  		final:  final,
  		notify: notify,
  	}
  }
docs: // New creates a new handler that guarantees all notify functions are run after the critical
  // section exits (or is interrupted by the OS), then invokes the final handler. If no final
  // handler is specified, the default final is `os.Exit(1)`. A handler can only be used for
  // one critical section.