head, tail, and recursive foldl
Merge pull request #2 from buzzdecafe/master

head, tail, and recursive foldl

This isn't quite what I was imagining, but it's certainly a good start.

I'm hoping perhaps that the public API would accept arrays and that they would be converted to list-wrapped arrays on their way in to the internals and then unwrapped if necessary on their way out.  Internally, everything would operate on list-like structures that were somehow backed up by these arrays.  But this is great as it stands.  That can wait.