Start of re-write with asyncio

[mdavidsaver]

The very incomplete beginnings of a re-write of recceiver with python3+asyncio. Covers the recsync protocol and little else. Something I started last year, partly as an exercise in exploring some python3 features (so be warned!). I've gone back and added some comments and TODOs. I'm not sure when/if I'll get back to it. I'm posting it here on the chance that it helps someone else get started, either by extending this code directly, or only taking it as informational.

I've had some good recent experience with aiohttp, which I'd suggest looking at instead of the blocking pyCFClient.

(adding this as a recceiver2 package is entirely a temporary measure. I tend to do this so I can continue to refer to the current implementation. If/when finished, I'd rename/replace as recceiver)

[sonarqubecloud]

Quality Gate failed

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