Updated DataStrucutres/binary_search_tree.py to improve clarity.

Replaced obscure member names like 'r' and 'l' with clearer options ('right', 'left', etc.), updating comments as required.
Updated DataStrucutres/binary_tree.py to improve clarity.

Replaced obscure member names like 'r' and 'l' with clearer options ('right', 'left', etc.), updating comments as required.