Merge into nix

[Susurrus]

I'm posting here to see if there's any interest in getting this merged into nix as it would be suitable to merge. A user posted an issue for adding this feature to nix (nix-rust/nix#601), but it's not on anyone's plate yet. I wanted to see if you'd be interested in merging this crate in with nix.

[viraptor]

I think I raised this idea at some point, but didn't have time to follow up. As far as I remember nix leadership want against it. If you'd like to do the work, I'd really appreciate it. Otherwise, I see there's some interest in this, so I can put it on my to-do list (no time guarantees though)

If anyone wants to do this though, it's probably a good time to sort out the constants names at the same time. I expanded some cryptic ones, but preserved other as they appeared in the headers. Going 100% either way could be better.

[viraptor]

s/want against/wasn't against/