NB. This crate is a proof of concept and is not supported.
A futures 0.3 executor, built to avoid leaking shared data in futures.
The threadpool in futures (https://rust-lang-nursery.github.io/futures-api-docs/0.3.0-alpha.13/futures/executor/struct.ThreadPool.html) uses Arc to share futures in Waker. This can lead to a non-0 strong count after the pool is dropped.