Yet another string interning library

Part of the rerun family of crates.

String interning is a way to reduce memory use by detecting duplicated string and storing them only once.

The main thing that makes this library different is that InternedString stores the hash of the string, which makes using it in lookups is really fast, especially when using nohash_hasher::IntMap.

The hash is assumed to be perfect, which means this library accepts the risk of hash collisions!

The interned strings are never freed, so don't intern too many things.