Extended two class templates from BST repo.

benchtree: C++ program benchtree that permits benchmarking the performance of 
a RST implementation, an ordinary BST implementation, and the
C++ STL std::set structure. "performance" means "how many comparisons were 
required to do a successful find operation, in the average case"

benchtree takes four command line arguments:
1. string which must be either "bst", "rst", or "set", and indicates whether
   benchmarking should be done using a BST, a RST, or std::set.
2. string which must be either "sorted" or "shuffled", and indicates whether
   the keys inserted in the structure are inserted in sorted order, or
   shuffled (randomized) order.
3. integer which specifes the maximum size of the tree to be built in the
   benchmarking. Trees should be build with sizes N that are a power of 2,
   minus 1, in the range 1 up through this maximum size.
   This permits comparing results to the 'best possible' binary tree with
   size N, a completely filled tree, which will always have a size that is a 
   power of 2, minus 1.
4. integer that specifies how many runs will be done, and averaged over, for each N