Add asyncio events module

[bdraco]

This is the module being used in Home Assistant and pysonos (https://github.com/amelchio/pysonos/blob/master/pysonos/events_asyncio.py) with the extras stripped out modified to work on python 3.5+.

[bdraco]

There is a case where I/O can happen in the event loop discovered in home-assistant/core#48732 though which affects twisted as well.

I'll push another change to fix that but twisted likely needs a similar fix to run it in twisted.internet.threads.deferToThread

[pwt]

Hi @bdraco:

Thanks for this great contribution. I'm optimistically targeting its inclusion in the upcoming v0.22 release (17th April).

I'm going to continue to review and make comments. Please excuse me making comments in multiple passes ... I only have a superficial knowledge of asyncio.

Edit: Also, I realise that some of the review comments could equally apply to some of the existing code; I just want to make new code as clean as possible.

[pwt]

I've pushed the changes I proposed in my review to your branch (a0303a6). Feel free to review and revert, of course.

[bdraco]

I've pushed the changes I proposed in my review to your branch (a0303a6). Feel free to review and revert, of course.

Nice! LGTM 👍

[pwt]

I think this is ready to merge, but I wouldn't mind another set of eyes on the changes to events_base.py in particular. (@KennethNielsen if you have time perhaps you could take a quick look. No problem if not.)

In the absence of further comments, I plan to merge this in the next few days, for inclusion in v0.22.

[bdraco]

Thanks!