Draft a full zsh completion

[desertstsung]

Major change:
draft a (probably) fully documented zsh completion

Minor changes:
1.change -l on into --label on in tools/chafa/chicle-options.c
2.change some options' alphabet order option_entries in tools/chafa/chicle-options.c
3.change --label and --grid options description, and add -l and -g alias options description in docs/chafa.xml

@hpjansson please have a review, thank you.

[hpjansson]

Looks good! Thanks for catching the documentation inconsistencies too.