Ctrl-C does not work on Windows

[dgw]

As touched on in my approval of #1381, Windows doesn't support SIGUSR1. Sopel's signal handler unsafely handles all signal types in one if ... or ... line, and crashes with an AttributeError on Ctrl-C because of the reference to a missing signal type.

What's fun is that Sopel's threading prevents the exception from terminating the whole program anyway. So, Ctrl-C is pretty well broken on Windows (at least on Win7, the only version I have available).

I'm putting this in the 6.6.0 milestone just for visibility, but it can just be punted to the next release if not fixed in time. It's been around for at least 5 years already, and not many Sopel users (anecdotally) run Windows. (I'm not fixing it immediately myself because, well… Windows. Meh. 😹)

[dgw]

We'll worry about this later. At present I can't even get Python installed on my Windows machine to check if this is even still a problem. Someone else feel free to test, but any fix that might be needed for this is officially punted to 7.1 no matter what.

[dgw]

Let's not look into this until we drop old Python releases for Sopel 8. This might be fixed in currently-supported versions on Windows, or at least might be easier to debug with a smaller target range.

[dgw]

We still don't have much motivation to worry about this, given the existence of WSL. Dropping to wishlist.