In clap 3.0, it's no longer possible to get `App::write_long_help` to
output colorized text (it doesn't invoke the Colorizer at all). So let's
move the generation outside of Rust.
This partially addresses #33, and allows Colmena to be used more
easily on bandwidth-constrained hosts and macOS.
With `deployment.buildOnTarget = true;` deployment works fine from
macOS without designated builders, except when IFD is involved.
Nixpkgs now includes Colmena starting with 21.11 and is now the
preferred method to obtain Colmena. The `stable` branch will
continue to be updated for each stable release.
Fixes#41.
