DataStructures/Trees/BST.h: Builds upon the new BTNode class to create a new data structure, the binary search tree.

DataStructures/Trees/BTNode.h: A building block for binary tree-based data structures (binary tree, binary search tree, etc.).

README.md: Added TODO notes about trees, graphs, commenting, and class design.

DataStructures/Linear/LinkedList/LinkedList.h: Rearranged header includes.

DataStructures/Linear/LinkedList/LLNode.h: Rearranged header includes.