Include sections into final file depending on section's indentation in main.yaml

[kvaleev]

Sections that are indented into the main.yaml file should be included into a final document with a heading level, that depends on indentation: every indentation level adds an additional level of heading.

For example:

---
chapters:
- intro
- section-main:
    - section_1
    - section_2
...

Here, all headings in section_1 and section_2 files will be increased by one level.

If heading level in the final file will be more than 5 — heading should be replaced with bold.

[Vanderhoof]

That's a cool feature, we should do it for Pandoc!