Flatten Binary Tree To LinkedList In-Place

	/**
	 * Given a binary tree, flatten it to a linked list in-place.
	 * 
	 * For example, Given
	 * 
				      1
			        /   \
			       2     5
			      / \     \
			     3   4     6
			    / \   \   /
			   7   8   9 0
	 * 
	 * 
					   1
					    \
					     2
					      \
					       3
					        \
					         4
					          \
					           5
					            \
					             6
	 * 
	 * */