implemented rotate_left
Merge branch 'master' into redblack
fixed rotate_left & added test
added right red check
rewrote _has_right_red
added symmetric check
rewrote symmetric check
added color_flip
moving _symmetric to base
Merge branch 'master' into redblack
Merge branch 'master' into redblack

Conflicts:
	test/test_bst.py
scope fixes in BST, RedBlack.add, some client code