Split the spec into two

[Felix Queißner]

> Yeah, this makes sense.  I hadn't really thought about it, but the
> text/gemini spec is kind of smack bang in the middle of the other stuff.
Yeah, it's not always obvious when working a long time on some stuff.
All relevant information is there, but there is stuff added and removed
and one misses the bigger picture sometimes.

> I still think it's a good idea to have everything in one place, but some
> rearrangement would not hurt.  I will try to do this tonight.
Nice, thanks!

Regards
- xq