process_one only accepts coroutines for dispatch

[minrk]

closes #860

alternately: make the await dispatch check inspect.isawaitable before awaiting.

[blink1073]

I'm not sure how asyncio handles an async function that is used as a callback to call_later, it doesn't say in the docs. I think the alternate approach you mentioned is safer.

[minrk]

call_later isn't getting an async function to call. call_later is being passed the synchronous schedule_dispatch function to call, with the async function passed as an argument, eventually to be called and awaited by us here.

[blink1073]

Ah, understood, thanks!