Build complete binary tree from LL

http://www.geeksforgeeks.org/given-linked-list-representation-of-complete-tree-convert-it-to-linked-representation/

Signed-off-by: Vidhoon Viswanathan <vidhu2366@gmail.com>
Merge branch 'master' of https://github.com/vidhoonv/interview_prep

Signed-off-by: Vidhoon Viswanathan <vidhu2366@gmail.com>

Conflicts:
	gfg/trees/tree_from_LL.cpp