NodeStack<E> a generic stack

The NodeStack is an implementation of a stack of a generic type.
The stack is implemented using, essentially, a generic linked list
of reduced functionality (made up of generic nodes).

NOTE:
  - The NodeStack cannot explicitly generate a stack overflow
  - The NodeStack is visually reversed with respect to the ArrayStack
  - What are implication of pop with respect to garbage collection (gc)?
  - Can we make NodeStack "greener", and if so, how?
    - see GreenNodeStack and GreenTest

The program Test.java allows us to play with a stack of String.

It would be nice to modify Test to give IntTest, using the NodeStack<Integer>

NOTE: this code corresponds to Goodrich & Tamassia (4th ed) Chapter 5, pages 197 to 198

Patrick Prosser
14/01/2011