Alternative to priority_queue dependency

[glittershark]

dc78d2d added a new dependency on the priority-queue crate, which is LGPL licensed - unfortunately, since Rust statically links all libraries and we distribute binaries to customers, this currently likely prevents us using mysql_async past that commit. Is there a world where you'd consider an alternative to that dependency, either permanently or via a feature flag, to allow non-copyleft-compliant use of mysql-async?

[blackbeam]

Oh, thanks for pointing it out!
@cloneable, could you please come up with a replacement?

[cloneable]

Sure! Technically, p-q is also licensed under MPL2, but I'm going to look for an alternative. Maybe the wait queue can be replaced with a tokio semaphore based queue.