rename kind to variant, colors to palette

This is to fit in better with tinted theming's terminology.

allow custom logo colors (#46)

alias lib-core to lib, lib-contrib to lib.contrib

As promised on 2.0.0 release notes. This is marked as breaking change,
although people migrating from older than 2.0 version might have
some trouble (as lib was previously a function and is now a regular
attrset).

format with nixpkgs-fmt

remove deprecated runCommandNoCC

fetch schemes from base16-project, reorganize lib

This is a major change, but the only breaking change is the lib function namespace.

You can now use either nix-colors-style schemes, or base16 YAML schemes directly, using the new `schemeFromYAML` function.

Opinionated functions have been moved into `lib-contrib`.

base16 has moved to an org, so with that in mind we no longer need to vendor schemes here.

Docs has been updated, and the repo was cleaned up from now-unneeded stuff.

All occurences of "color(S|s)cheme(s)" have been normalized to "colorScheme(s)", with "colorscheme(s)" as aliases.

Changelog:
- Add `schemeFromYAML` and `schemeToYAML` functions.
    - These are pure nix, and allow us to finally use base16-project's `.yaml` schemes without requiring users to pass `pkgs` or specify `system`.
- Use base16-project scheme repository. There is a scheme monorepo now, which makes our lives a lot easier
    - We no longer vendor schemes.
    - The schemes we previously had were upstreamed on tinted-theming/base16-schemes#1
- Move opinionated functions into `lib-contrib`
- Update docs
- Clean up repo

Add PaperColor Theme (#13)