Async Pest

[ekechinwokah]

Hi - made some changes to use pest in async, largely borrowed from this code discussed in a previous issue.

Is there any interest in merging into the master branch? Either way is fine but wanted to check.

[NoahTheDuke]

It looks like the only changes is from alloc::rc::Rc to alloc::rc::Arc? I think that's a breaking change as the Rc usages are on public-facing apis (structs and functions), and I don't know that we can make such a change without a major version bump.

I wonder what kind of benchmark hits this results in. How much slower is Arc than Rc in Pest?

[ekechinwokah]

Ah, got it. We haven't benchmarked.