Composable folds using an applicative interface for OCaml.
For a demo, see demo.ml. You can validate only one call to List.fold is
performed by running make and taking a look at validate.ml and
_build/validate.s.
This is based on work by Gabriel Gonzalez, see http://www.haskellforall.com/2013/08/composable-streaming-folds.html.