guix fish completions (preview)

[ng0]

I'm not up to releasing it, as some functions (like guix pack)
are missing now, and some are not complete. I want at least 98% complete
coverage of guix before I make a release.

fish-guix was started as a 'pet project' to hack on guix completions for
the fish. For those who want to test it, it's located at:
https://gitweb.pragmatique.xyz/user/ng0/fish-guix.git/

The way I usually do commits ignores the git feature of added metadata
tracking, when you are active working, and other patterns. It might say
"last commit 32 years ago", and there's only two commits, but I squashed
most commits together as I moved it from its previous location.

I welcome contributions of any kind via plain git send-email or whatever
applies, pulling from remotes, etc.

On the occasions where I used fish, this was already helpful and
functional.

The way these fish completions work, is by cloning it and then
symlinking into the fish/completions directory.