Module Trie

module Trie: sig .. end
Trie over lists of values

Tries in this implementation contain data at the leaves only. An inner node contains only the subtries for each key.

This module is inspired by Jean-Christophe Filliatre's implementation at
Author(s): Christoph Sticksel

module type S = sig .. end
Output signature is an extended map
module Make: 
functor (Ord : Map.OrderedType-> S with type key = Ord.t list
Trie over sequences of keys of map