Add `sort` function to `std`

[TheLostLambda]

Not certain which algorithm we'd want to use, but I was very surprised to not find any sorting functions in std! It seems like a super common operation and there are a number of algorithms already in the tests/ folder.

Is there a reason these haven't been added already? Is it the sort of thing that you'd be interested in me adding via a PR?

P.S. Koka is probably the most elegant language I've ever come across — it's very exciting to see so much innovation in the functional programming space and research put into practice!