Yet another WaitGroup implementation.

None of the existing crates fit my needs exactly, so here's one more that (hopefully) will.

Highlights:

• Generalizes "tasks" to Refs. More of a change in nomenclature than anything else. It's not always a group of tasks you're waiting on - it could be that you're waiting on a gaggle of structs to all be dropped.
• Refs and Waiters are entirely disjoint. You don't need a Waiter to create a new Ref.
• Everything is cloneable and behaves as one would expect - cloned Refs will all block every cloned Waiter, which can be awaited concurrently.

License

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in tokio-core by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.