Sorted Containers

Added sorted containers to DataStructures, testing, and documentation.
Replaced README.md with README.rst
Kevin,

I did not know about "for p in m" because it is not in the manual as far as I can see.  On the other hand, "for p = m" is in the manual in the appendix under the heading "Iteration" in the chapter called "Standard Library."  Therefore, I would be happy to switch my code if someone (perhaps me? you?) submits a request to edit the manual to include the alternate syntax.