Add list-permute

[soegaard]

Note that immutable? returns #f for lists, so there is no immutable? in the contract for list-permute.

[jackfirth]

@soegaard I was able to implement a permuting transducer that can permute arbitrary sequences, and using that, I made a permute function that accepts any sequence and optionally lets you customize the output reducer. Here are some equivalences:

• (vector-permute vec p) == (permute p vec)
• (list-permute lst p) == (permute p lst #:into into-list)
• (string-permute str p) == (permute p str #:into into-string)

I want to eliminate the type-specific permutation functions to keep the API simple. What do you think?

[soegaard]

A general permute sounds like an excellent idea.