stack.go
func (stack *Stack) Push(entry interface{}) {
	stack.key.Lock()
	defer stack.key.Unlock()

	if nil == stack.underlyer {
		stack.underlyer = NewLinkedList()
	}
	stack.underlyer.AddFront(entry)
}
func (stack *Stack) Push(entry interface{}) {
	stack.key.Lock()
	defer stack.key.Unlock()

	if nil == stack.underlyer {
		stack.underlyer = NewLinkedList()
	}
	stack.underlyer.AddFront(entry)
}
// Push adds an entry to the top of the Stack.