bash/zsh completion for the catmandu command

[nics]

[jorol]

See spec and talk from @perlpunk:

https://github.com/perlpunk/App-Spec-p5

https://github.com/perlpunk/myslides/blob/master/app-spec/slides.vroom

[nichtich]

To me this seems to be the most important open issue for better usability of the CLI but it likely requires some major refactoring.