Search GUS by content type!

[Natalie Pendragon]

Hi everyone,

I just wanted to share a nice update on GUS. After some discussion
with sloum, I decided to put some time into better support for content
types.

Content types been being printed alongside search results for a few
weeks already, but I'm happy to announce that as of today you also get
first-class support for them in your queries! There is documentation
for how to use them at gemini://gus.guru/about, along with a number of
useful content types to try out, like audio, image, and text.

One of my favorite so far is `audio`. You could search for, say,
`content_type:audio` to find ALL music in Geminispace, or `dogs
content_type:audio/mp3` to find some good songs about dogs in mp3
format.

Thank you for all the feedback on this project so far. I still have a
nice list of TODOs for GUS, mostly due to conversations with other
Geminauts.

Nat