beekeeper: an ergonomic workerpool crate

Hi r/rust! I've just published beekeeper, a workerpool library written in Rust.

This crate started as a fork of workerpool, but at this point it's pretty much a re-write and has lots of additional features, including:

• A Worker trait that is not required to extend Default
• The ability to write workers with mutable state
• Support for custom worker factories
• Stock worker implementations, including support for parallelizing callables (functions or closures)
• Methods for submitting batches of tasks
• The ability to retrieve results as either ordered or unordered iterators, send them to a channel (with support for several alternative channel crates), or store them in the workerpool data structure (called a Hive) for later retrieval
• The ability to pause and resume processing
• (optional) support for automatically retrying failures
• (optional) support for pinning worker threads to CPU cores

I'd love for you to try it out and give feedback about what could be improved.

Enjoy!