All module options are now settable through the freeform `.settings`.
- Mikutter was removed because the package was broken and had no maintainers.
- Gollum was upgraded to major version 6. Read their [migration notes](https://github.com/gollum/gollum/wiki/6.0-Release-Notes).
- The hooks `yarnConfigHook` and `yarnBuildHook` were added. These should replace `yarn2nix.mkYarnPackage` and other `yarn2nix` related tools. The motivation to get rid of `yarn2nix` tools is the fact that they are too complex and hard to maintain, and they rely upon too much Nix evaluation which is problematic if import-from-derivation is not allowed (see more details at [#296856](https://github.com/NixOS/nixpkgs/issues/296856). The transition from `mkYarnPackage` to `yarn{Config,Build}Hook` is tracked at [#324246](https://github.com/NixOS/nixpkgs/issues/324246).