Remove the llrb tree, moving to redblack/ under smap/
Remove the Scanner interface from smap
Expose Interval and smap.Scan(Interval) -> Iterator
Remove Close() from smap.Iterator
Add Key() method to iterator, we need both keys and values
Move inOrder traversal to helper_test.go, only used in tests
Add more thorough tests on range scans and fix issues on open intervals.