Sniff out which async library your code is running under
Description
You're writing a library. You've decided to be ambitious, and support multiple
async I/O packages, like Trio, and asyncio, and ... You've written a bunch of
clever code to handle all the differences. But... how do you know which piece
of clever code to run? This is a tiny package whose only purpose is to let you
detect which async library your code is running under.
