Async requests

[MiWeiss]

Exposing async interfaces would allow using this library in a much more modern, performant, and scalable way.

Would be great if the maintainers could mention if they plan to add async methods in the future (i.e., allow for nonblocking api usage). Even specifying explicitly that this won't be added would be great, as it allows 3rd parties to release their own fork or wrapper, without the risk of being obsolete just moments later :-)