Parallel map on node.

[ngoodman]

It would be neat to have p-map available (at least when run via node on server). This simply runs a thread (or node process) for each item in a list, applying the given (purely functional) procedure.

Very useful for running an inference over a range of param values.

Possibly useful for speeding up inference for some "big data" (shallow but wide) models, depending on communication latency.