add unit test frameworks to list
implement bt_print and finally test the tree in main (since I can print now)
update bt_print doc comment
augment printing with edge labels, add insert/remove tests in main
implement bt_size
reorder define macro
implement tree depth calculation
reorder bt_print to match header file
implement contains
begin implementation of rebalance tree - flatten the tree into an array of sorted nodes
first stab at a rebalance algorithm (not tested, probably wrong)