Create Populating Next Right Pointers in Each Node.cpp

Basic Idea: breadth first traverse. 
prevQueue remembers TreeNode pointers found in last level lookup.
currQueue remembers TreeNode pointers found in current level lookup.
when popping out a TreeNode pointer from prevQueue, we set up the next pointer of that TreeNode pointer. We do not need to set the last TreeNode->next to be NULL because its constructor did it for us.