added publish async

func slowCalculator(a, b int) {
	time.Sleep(3 * time.Second)
	fmt.Printf("%d\n", a + b)
}

 bus.Subscribe("main:slow_calculator", slowCalculator);
 bus.PublishAsync("main:slow_calculator", 30, 70);
fmt.Println("waiting for result")

bus.WaitAsync();

bus.Unsubscribe("main:slow_calculator");