Packaging modernization needed

[dgw]

I can't get to all of the plugins at once, but I intend to get to them all Eventually™ and creating an issue that I can self-assign helps with that. This plugin also doesn't cap the version of sopel it requires to <8, so it won't refuse to work on the new Sopel 8 release or cause pip to silently downgrade an existing bot—which pushes it down the priority list, below other plugins that do do that.

(The project doesn't collect any analytics, so we have only anecdotal evidence and guesses to figure out which plugins are frequently used. Guessing is probably good enough. Probably.)