Add sorting

No response on the [mailing list](https://groups.google.com/forum/#!searchin/elm-discuss/sorting/elm-discuss/Isjm69tmbec/VV_0coCn3xAJ) so I'll just leave this here. Let me know if you want the contributor agreement or a different target branch.

The code itself is pretty straightforward, and basically just accounts for the currying of `Utils.compare`.