Help wanted

[withoutboats]

In the medium term, I want to pass maintainership of this library to other people. Here are some things that need to be done that I have no intention of doing:

1. Documentation for all of the APIs in the library.
2. Benchmarks to get a sense of performance bottlenecks in the implementation.
3. Making the API equivalent to std's API.

Note on 3: it's good to look at dashmap for API differences between a concurrent hashmap and a nonconcurrent one. Also, though, I think we should avoid exposing dashmap's types, or any APIs that reveal dashmap's structure (like the shards API), so that waitmap can replace that implementation as needed (e.g. upgrading across breaking changes to dashmap should not be a breaking change to waitmap).