Add tests for Bst.in_order() to assert that the in_order generator yeilds tree values in numerical order
Add Bst.in_order() to return a generator that yeilds all tree values in numerical order
Resolve merge conflicts in bst.py and test_bst.py
Add dependencies
Add test for Bst.pre_order()
Add Bst.pre_order() and Bst.post_order() to return generators with nodes traversed in respective order