Created RBTree.h

creates class RBTree which holds one private element that is the root of the tree and many public functions that help build the tree. 

-the print function prints the tree in preorder which prints an ordered binary search tree
-the addNode function creates a new node with the new data element included in node and then finds the correct location in the tree to insert the node. it then rearranges the trees children and parents accordingly. after that, it rebalances the tree by calling the fixTree() function
-the class contains accessor functions for the tree's aunt, sibling, and grandparent node. 
-rotateLeft and rotateRight function follow standard rotating algorithms that rotate left or right about the root node. 
-fixTree checks if the tree is unbalanced and does the necessary corrections.