Goal:

Write a simple shell that takes in data as strings, 
puts it into a binary tree, and then allows the user
to list the tree in preorder, postorder, and inorder;
and to add and remove further nodes, to duplicate the
tree (single-letter case-insensitive names), sort a
tree, reverse (mirror) a tree, balance a tree (also
done when sorting a tree), ask for the size, depth, 
and width.