Deprecation of `asyncio.get_event_loop()` if there is no running event loop

[stfwn]

Hi! Thanks for writing and maintaining this module! :smile:

The Python 3.10 docs for asyncio.get_event_loop() note:

Deprecated since version 3.10: Deprecation warning is emitted if there is no running event loop. In future Python releases, this function will be an alias of get_running_loop().

It seems @async_handler will fail with RuntimeError: no running event loop in that case. Do you think this correct?

Perhaps a solution is to effectively move the deprecated functionality into the module itself. I created a PR for this.