Cooperatively working with "async-recursion" crate

[Tarbetu]

Hi!

I like this project, however I have to say that requirement for "async" also brings the need for async-recursion crate because the recursion in async functions are forbidden by the compiler.

"Ctx" also needs a lifetime declaration, and it complicates the situations with this crate.

You might provide more documentation for possibly pitfalls and caveats while using "async-recursion"

Thank you.

[DelSkayn]

It does indeed currently require async-recursion crate but in the upcoming beta version 1.77 the restriction which forces you to use async-recursion will be lifted. So this PR.

I had locally already changed the minimal supported rust version to 1.77 but I see I haven't yet pushed that change.

Note that this is still a very much in development library so expect some cruft here and there.