Allow headers to define sections

[adamant-pwn]

For larger sites, whole navigation table could take much more than a single screen. It would be very nice if using headers at least for top-level sections is allowed. So, e.g.

# section 1
    - subsection 1
        - [article 1](...)
        - [article 2](...)
    - [article 3](...)
# section 2
...

Ideal scenario would be to allow freely changing between headers and lists.

[oprypin]

This makes sense to me. Just seems painful to implement