The stub of append() should look like this:
   void List::append(const Item& it) {
The steps append() should take are:
  1. Dynamically allocate a new Node in which myItem is it and myNext is NULL; save its address in nodePtr.
  2. If I am empty: Otherwise:
  3. Make myLast point at the new node (using nodePtr).
  4. Increment mySize.