* add second build target `world.c`
* add GitHub workflow to build all targets, upload/publish all artifacts
  * deb, rpm, tgz of source
  * Docker container on DockerHub, GitHub Container Repository (ghcr.io)
    * containers could have multiple tags as in `latest` and `1.0.0`
* add Nix Flake
* devshell
* direnv/envrc
* build windows MSYS2
* formatting
* lint
* security audits
* Gitpod