No need for brittle regex when matching plain strings or domain names.
This should save some negligible amount of heap memory as well as
tremendously speeding up the matching.
It was added in 2022 by #1513, to support blog.laravel.com, which has
since switched to HTML. The Atom 0.3/1.0, RSS 1.0/2.0, RDF, and JSON formats
don't support markdown in their spec, and any website serving it there should
be considered as buggy and fixed.
This shaves off 2MB from the miniflux binary, which is quite steep for a
feature that nobody is/should be using, and remove a dependency which is always
a good thing.
By default, Oglaf show some disclaimer/warning about its content, and this
doesn't play well with rss readers, so let's rewrite it to show the actual
comic instead of a placeholder.
