Missing async support (async-std + async adapter)

[GopherJ]

casbin and diesel-adapter are synchronous, but it's worth adding async support to casbin and create a new async adapter.

https://github.com/async-rs/async-std
https://github.com/launchbadge/sqlx

The new adapter can be called sqlx-adapter, it's not ORM, but it's full asynchronous.

[hsluoyz]

lgtm!

[GopherJ]

async-std has been added to casbin-rs in #53

[GopherJ]

sqlx is not very mature at this point, I'll add a sqlx-adapter later. Now we stick to https://github.com/casbin-rs/diesel-adapter

[GopherJ]

actix-web uses tokio as runtime, it's important to keep the async-std runtime and to add another feature called runtime-tokio. So that casbin-rs can works asynchronously in actix-web.

[mehcode]

sqlx is not very mature at this point [...]

@GopherJ Is there something in particular you were missing from SQLx? Happy to help prioritize any remaining pieces.

[GopherJ]

@mehcode @hackerchai is working on it and I think he has already everything he needs. So it's fine:) Thanks for making this cool library.

[hackerchai]

@GopherJ @hsluoyz sqlx-adapter version 0.1.0 can be reviewed here: casbin-rs/sqlx-adapter#2

[GopherJ]

https://crates.io/crates/sqlx-adapter