range-map
This crate provides maps and sets where the key is a primitive integer type.
Whereas in general-purpose maps and sets performance generally depends on the
number of keys, here it depends on the number of ranges of keys. For example,
in this crate it's very easy to represent the set of all u32 values, but it
would be a bad idea to represent the same set using
std::collections::HashSet<u32>.