Use "include" preprocessor attributes in "chapters" block of foliant.yml

[v4dkou]

Consider adding YAML tags for "chapters" block that work as "includes" preprocessor
https://foliant-docs.github.io/docs/preprocessors/includes/

For example:

chapters:
    - Animals:
        - !set_head 2 elephant.md
        - lion.md

Temporary solutions
For now we use intermediate files like this

animals_index.md

# Animals:
<include src="elephant.md" sethead="2"></include>
<include src="lion.md" sethead="2"></include>