add contains method as given in notes
add getMax() and getMin() methods as instructed
add interface for the IntegerTreeNode
Test program for Integer Binary Tree.  Output...

$ java TestIntegerTreeNode
Created tree like in Notes Figure 2 with 6. 9, 5, 3, 11, 12, 8
check whether tree contains 11 (it does) gives: true
check whether tree contains 10 (it does not) gives: false
The maximum value in the tree is 12, getMax gives: 12
The maximum value in the tree is 3, getMin gives: 3