Procedural macro for the `#[async]` attribute.
This crate is an implementation of the `#[async]` attribute as a procedural
macro. This is nightly-only for now as it's using the unstable features of
procedural macros. Furthermore it's generating code that's using a new
keyword, `yield`, and a new construct, generators, both of which are also
unstable.
Currently this crate depends on `syn` and `quote` to do all the heavy
lifting, this is just a very small shim around creating a closure/future out
of a generator.