Hash table with consistent order and fast iteration.
The indexmap is a hash table where the iteration order of the key-value pairs
is independent of the hash values of the keys. It has the usual hash table
functionality, it preserves insertion order except after removals, and it
allows lookup of its elements by either hash table key or numerical index. A
corresponding hash set type is also provided.
This crate was initially published under the name ordermap, but it was renamed
to indexmap.