Sorted Containers

Added sorted containers to DataStructures, testing, and documentation.
Replaced README.md with README.rst
Going back to the original point here: can you explain more clearly why you think that `isequal` can't be the default form of equality here?  (I have a vague recollection of you bringing this up on the mailing list, so feel free just to point me there).

The main reason is, again, that this is not considered a concern in the sorting code, which suggests that either it should be considered there, or that it shouldn't be a concern here (or that the sorting code takes care of the issue in other ways).

Not sure if this is entirely related, but I do know that equality has been discussed at great length previously.  The original epic was here:
https://groups.google.com/forum/#!searchin/julia-dev/john$20cowan$20egal/julia-dev/d9aE-njMRU4/lotgP16ePWsJ