[2.0.0] Move out of the io.github.betterthanupdates package

[halotroop2288]

I've started putting Better Than Updates projects under the com.halotroop.btu package as that's where I prefer to put the documentation.

Since this project is now owned by Fabric Compatibility Layers, I suggest the com.halotroop.fcl package, and I can host the documentation at fcl.halotroop.com or halotroop.com/fcl

If that doesn't suit this project, we can just use io.github.fabriccompatibiltylayers.

[thecatcore]

Moved to io.github.fabriccompatibiltylayers in 2.0.0

[thecatcore]

Oh wait I think I forgot to commit this