Added AVL Tree#23

Merged

czgdp1807 merged 7 commits intocodezonediitj:masterfrom

czgdp1807:avl-tree

Oct 20, 2019

Commits on Jul 4, 2019

Commits on Jul 5, 2019

insert started
czgdp1807
committed

Commits on Jul 7, 2019

Commits on Oct 8, 2019

testing complete, few corner cases still left
czgdp1807
committed

Commits on Oct 20, 2019

avl tree complete, minor coverage left
czgdp1807
committed