RSS is a tire fire

Some readers take images out `CDATA` HTML fragments in the description, ~~but fuck those readers~~ we now support them too.

Here, I add the `<enclosure ...>` for an image, and hope that the world doesn't burn down.

Because of our run-in with PNG, and because I don't want to think about it ever again, ~~I'm leaving the mime type open~~ I've fixed the mime type detection in the RSS feed.

**Fuck. Computers.**