async_std port

[pferreir]

Hi there,

Thanks for this great lib. I happen to have ported it to async_std, which was not too hard to be honest. Would a PR be of interest to you? In that case, should I make it a cargo feature (default could still be tokio)?

[dblsaiko]

Since this crate seems unmaintained right now, I have published mumble-protocol-2x which has both async_std and tokio support (toggleable via features).