stack method

* create
* iterator (N/A)
* add
    * push: Adds the element at the top of the stack.
* change (N/A)
* query
    * empty: Returns whether the stack is empty.
    * size: Returns the size of the stack.
    * top/peek: Returns the top most element of the stack.
* delete 
    * pop: Deletes the top most element of the stack