compgen command

[ken-matsui]

It would be great if we could generate shell completions for major shells using and modifying CLI classes, similar to clap_complete. This command is intended for use by package managers, such as Homebrew, during the installation of Poac, not for typical end users. Therefore, it would be preferable to hide this command by default, like we do for some options.

https://github.com/poac-dev/poac/blob/7c4f62ef0902c763571cff39576c46c2bccb8827/src/main.cc#L22-L25

https://github.com/poac-dev/poac/blob/7c4f62ef0902c763571cff39576c46c2bccb8827/src/Cli.hpp#L61-L64