Crate immutable_chunkmap

A cache efficient immutable map with lookup performance equivalent to BTreeMap, and reasonably good insertion performance (for a persistent structure). The Rc versions cannot be used by multiple threads at once, but have slightly lower single threaded overhead. Each module is duplicated for rc/arc. e.g. rc::map uses Rc, arc::map uses Arc.

Modules

arc	chunkmap using Arc pointers
rc	chunkmap using Rc pointers