Sorted Containers

Added sorted containers to DataStructures, testing, and documentation.
Replaced README.md with README.rst
> [Note to David Sanders: If you send me your email address, I can directly
cc you on my messages sent to github.

Now that David has commented on this PR, he should get a copy of all messages.

David, I've edited your comment on github to remove the quoting, so it should be easier to read.  You can do the same with your own comments if you use the github interface.  (Are there other comments that you think need cleaning up?)

Note that if you use the github interface directly, you'll have access to markdown, but email replies will appear however the responder formatted them.

> Let me know which of these (token, address, handle) you like best.

I agree that any of the three will work.  I think I like token the best, if only because it's shortest.

> They wouldn't opt for the extra complexity of setting up a `SortedDict` in the first place unless they already needed the extra functionality of iterating in sorted order.

I absolutely agree.  I guess it depends on the user's use case.  I have had situations where all I wanted was to have a dictionary which kept sorted order while inserting items, and over which I could then iterate in sorted order.  

My interpretation of your perspective is that you want to iterate over a dictionary, and update values during that iteration using the returned token.  Is this correct?

If so, I can see the usefulness in using tokens.  Perhaps all that is needed is a different interface.  I'll propose that below.