Sorted Containers

Added sorted containers to DataStructures, testing, and documentation.
Replaced README.md with README.rst
Obviously, the type parameters here restrict objects of this type to belong to a `SortedDict` with the same key/value types.  For me, they seem extraneous--I think any error a user would make in using this would be caught as soon as they tried doing anything with the relevant key or value, and that too many type parameters clutters the code.  But I haven't done much C++ programming recently. ;-)