Add support for automated menu creation

[jaapio]

Feature request

Markdown doesn't have anything like a .. toctree:: in ReST This is not very nice as it requires a lot of hand work to create navigation. We want to provide an equal syntax as available for ReST to build navigation menu's

[jaapio]

Possible related topics are:
https://commonmark.thephpleague.com/2.5/extensions/attributes/

[jaapio]

Maybe this is a nice notation to inherit: https://github.com/markdown-it/markdown-it-container

[jaapio]

because markdown doesn't have a real standard but about 13M flavors: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts

[jaapio]

https://docs.gitlab.com/ee/user/markdown.html#table-of-contents

[jaapio]

https://rawgit.com/fletcher/MultiMarkdown-6-Syntax-Guide/master/index.html