func (s *simpleStack) Size() int {
	return len(*s)
}
Size returns the amount of elements in this Stack.
package stack
type simpleStack []interface{}
func newSimpleStack() *simpleStack {
	return &simpleStack{}
}
func (s *simpleStack) Push(element interface{}) {
	*s = append(*s, element)
}
func (s *simpleStack) Pop() interface{} {
	if s.IsEmpty() {
		return nil
	}
	index := len(*s) - 1
	element := (*s)[index]
	(*s)[index] = nil
	*s = (*s)[:index]
	return element
}
func (s *simpleStack) Peek() interface{} {
	if (*s).IsEmpty() {
		return nil
	}
	return (*s)[len(*s)-1]
}
func (s *simpleStack) Clear() {
	for index := range *s {
		(*s)[index] = nil
	}
	*s = (*s)[:0]
}