Async/await support

[tvolk131]

I'd love to see non-blocking I/O that works with Tokio! I don't know exactly how this would work under the hood, but I'm happy to look into it if you're interested.

[pleshevskiy]

Hello! Yes, I wanted to take the time to support async. I think it's low task because sonic doesn't support async yet.

[GallagherCommaJack]

i went ahead and implemented it anyway - probably makes sense to put async support behind a feature flag and open a pr?
GallagherCommaJack@5f94256

[pleshevskiy]

@GallagherCommaJack Very cool! Thank you for taking the time to do this. It is desirable to put async realization in a separate feature. there will need to be some fine-tuning if sonic gets a real async version, but that's not related to this PR

[pleshevskiy]

I'll start working on it after the #16