Replicate folder structure option for generate-ref script

**I'm submitting a...**

- [ ] Bug report.
- [x] Feature request.

## Feature request ##

Concepts of namespaces don't exist in GDScript, however, it's useful in an API reference to have sections separated by themes or namespaces, for specific areas of the API.

The generate-ref script could benefit from a "replicate folder structure" option, where the project's folder structure is replicated inside generated docs. It would allow large codebases API to be structured in the same way and be easier to navigate. Specifying a max-depth could also be useful, as one could just want to sort API docs by top-level folder structure.

Commencez par localiser le script generate-ref et lire comment il organise actuellement la documentation d’API générée. Définissez l’impact que la réplication des dossiers et une max-depth facultative devraient avoir sur la sortie, puis vérifiez qu’une grande base de code GDScript est organisée selon ses dossiers source sans modifier le comportement de génération existant.

Rédigé par le modèle d'indexation à partir du texte de l'issue.