MLstate/opalang — pull request #165 by mbouaziz (2014-11-19 14:19:51+00:00)
Title: Feature: multimaps

A `multimap(key, val)` is just a `map(key, list(val))`, mapping a key to several (ordered) values.
Added two efficient functions to use them : `Map.From.assoc_list_multi` and `Map.add_to_multi`