Support the trio event loop

[thedrow]

I'd very much would like to use this library but I use trio.
Using AnyIO instead of asyncio directly would enable using both asyncio (with or without uvloop) and trio.

[elprans]

It should be doable. Even asyncpg was made compatible with trio (https://github.com/python-trio/triopg), and edgedb-python has significantly less magic.