Motivation: There is a thriving plugin ecosystem for Kakoune now,
and it is nice to add these in our Nix configurations. This was modeled
on neovim's plugins.
parinfer-rust is useable both standalone and as a Kakoune plugin,
so the plugin file inherits the same definition as pkgs.
I'll make PRs for other plugins if this gets accepted.
[Here](https://github.com/eraserhd/nixpkgs/tree/kak-ansi)'s a tested
branch for the `kak-ansi` plugin.
* kakoune: Prefix version with 'v' (#50617)
Turns out there's some tooling parsing the version number and having a
'v' prefix works better in that case.
I tested that it builds & works fine on NixOS.
See: https://github.com/ul/kak-lsp/issues/99
* Override 'version' env variable
