Modernized packaging needed + Sopel 8 requirement bump

[dgw]

This plugin is likely nonfunctional, per #1, so this is a very low priority. But the current plugin version will forcibly downgrade an installed Sopel 8.x instance to 7.x because of its requirements, which is not ideal.

I propose modernizing the packaging on this plugin and adding a maintenance notice to the description, or formally archiving it if no interested party comes along to maintain it within some reasonable timeframe.