Currently, this crate contains a single type ListOrderedMultimap. This is a multimap meaning that
multiple values can be associated with a given key, but it also maintains insertion order across all
keys and values.
Nightly is required due to the use of the hashmap raw entry API.
Preliminary benchmarks show that performance is quite decent but more will be required to state anything definitive.
It is planned that a corresponding SetOrderedMultimap will also be included in this crate which
will provide the same insertion order guarantees, but the set of values associated to a given key
will be an actual set instead of a list.