hw#5
Due: 4/27/7

Use the implementation of binary search trees from class.

Write a function to compute the size of a tree based on the number of
nodes in the tree. Think of this recursively. The size of any tree is
somehow related to the current node and the size of its children.

Given this function, use it to implement a function "findkthsmallest"
which will find the kth smallest element in a binary search tree.