Added debug print helper for avl.c
Added debug printing for avl_find()
Added debug printing for avl_add()
Added debug printing for avl_del()
Added debug printing for insert_element_into_tree()
Added debug printing for destroy_subtree()
Added debug printing for rebalance_subtree()
Added debug printing for rotate_left()
Added debug printing for rotate_right()
Added debug printing for remove_element()
Added debug printing for isolate_root_node()
Added debug printing for isolate_leftmost()
Added debug printing for regen_metadata()
Added debug printing for find_node()
Merge pull request #151 from matthiasbeyer/add-debug_printing_avl

Add debug printing for avl