Sopel 8.0 update testing

[dgw]

This plugin will probably still work with Sopel 8 no problem, but it's been untouched for long enough that it deserves re-testing and some housekeeping.

Ideally, a new package named sopel-imdb would replace sopel-modules.imdb using entry-points instead of namespaces.

[dgw]

Just dropping a quick note that I reviewed this along with all the other plugin repos under @sopel-irc today, but didn't create a separate issue for packaging since this issue already mentions it.

I will tentatively assign this issue to @Exirel, as I heard he intended to look at modernizing this one.