Add a Table of Contents (TOC) custom block

[sylvinus]

Feature Request

Since the TOC was collapsed by default in the right sidebar it has become slightly harder to discover the content of long documents.

The TOC is also not part of exports, which could be desirable in some cases.

A good solution could be to create a custom bloc for a TOC that would be automatically synchronized with the titles from the document, and include anchor links to them. (dependency on #653 ?)

Thanks!

[virgile-dev]

Yep sounds like a good idea @rl-83 what's your take ?