[DRAFT] Add async/await support for oxide-auth-async

[FrancisMurillo]

This changes/fixes/improves …

• I have read the [contribution guidelines][Contributing]
• This change has tests (remove for doc only)
• This change has documentation
• Corresponds to issue ([QUESTION] How to integrate oxide_auth_async and oxide_auth_actix? #163)

Still fixing the main example work and adding another example to show explicit async/await usage

I license past and future contributions under the dual MIT/Apache-2.0 license, allowing licensees to chose either at their option.

[HeroicKatora]

On a general note: I'd actually rather replace the actix bindings with fully asynchronous ones rather than have two separate packages for it, if that sounds appropriate.

[FrancisMurillo]

On a general note: I'd actually rather replace the actix bindings with fully asynchronous ones rather than have two separate packages for it, if that sounds appropriate.

I tried doing in a separate crate first to see if there might be any issues with types and compatibility. I did have a problem with the actix actor example since the current implementation of Generic kinda needs to be Clone-able to pass the compiler check.

[FrancisMurillo]

@HeroicKatora So this is kinda my async use case. (Mine was diesel but wrapped them in async domain methods.) I think you can inspect the current example while I try to make the original example with Generic work if possible.

[FrancisMurillo]

@HeroicKatora Okay, I have tried several attempts to make Generic work within the async actix handler but its kinda tricky without creating thread safe versions generic components or removing the &mut in every Endpoint method which I do not think is ideal. So my current example I think is the easiest way I found so far.