Include headings level 3 in the menu, on click

[MariusDrulea]

Level 3 headings titles contain pretty important information as well and shall be outlined to the user for a better visibility. Maybe any heading shall be visible in the menu, regardless of the level. Shouldn't be an issue because these are displayed only on click. But at least Level 3 headings shall be included, see the use-cases bellow.

In Use-case1 the Debugger menu only shows Example, while important items like Ways to start the debugger are left in the page as details. It is clear the users miss this information, as we have to tell them over and over again to debug in the repl mode, see here: https://discourse.julialang.org/t/debugging-extremely-slow/53801/49.

In Use-case2 the Debugger menu shows Settings to speed-up the debugger. The options available shall be quickly visible in the menu: (ALL_MODULES_EXCEPT_MAIN, sys_images, Example).

Use-case1:

Use-case2:

[MariusDrulea]

@pfitzseb I haven't found a way to implement this, so you are free to do it 😄. Or at least give me a hint on how to implement it.

[mnemnion]

I've run into a similar issue using Documenter.jl. It can't be fixed directly: the sidebar displays level 1 and level 2 headers, and that's it.

But there is a workaround, which is what Documenter uses: break the files up like this, and "promote" the headers inside the file. That makes everything more fine-grained, with shorter, more focused topic pages.