How to close the goruntime in the pool

[wangxin0814]

`numCPUs := runtime.NumCPU()

pool := tunny.NewFunc(numCPUs, func(in interface{}) interface{} {
	intVal := in.(int)
	fmt.Println("first", in)
	time.Sleep(3 * time.Second)
	fmt.Println("second", in)
	return intVal * 2
})
defer pool.Close()

ctx, cancel := context.WithCancel(context.Background())

pool.ProcessCtx(ctx, 10)
time.Sleep(2 * time.Second)
cancel()`

first 10
second 10