Sorted Containers

Added sorted containers to DataStructures, testing, and documentation.
Replaced README.md with README.rst
At the time I wrote this, probably both, but...  I'm being tugged in a few different directions while reviewing this:

1. I want to give feedback quickly, so that you have something to work with.
2. I need to better understand your implementation, so that I can give good feedback, and this is taking some time.
3. I have other activities (work, family) competing for my time.

Whether these are a reason or excuse, I ended up skipping right past your explanation of indexes above.  Sorry about that.  I have further thoughts about them, which I'll make separately.