docs: Some restructuring

[LecrisUT]

I have caught an issue with the colon fencing breaking the set, while tick fencing works fine. But the section still feels off because the tabs are too big and specialized, e.g. it is not clear where warning applies or Writing metadata subsection. I think it would flow more clearly if we move it away to a separate document.

[henryiii]

Colon fencing has to have a blank line, like this:

Before

:::

Inside

:::

After

Otherwise the formatter messes it up. If you use tick-marks, then it is ignored by the formatter, some spell checkers, etc (because it's supposed to be code).

[LecrisUT]

Colon fencing has to have a blank line, like this:

I tried with various degrees of whitespacing until I was able to confirm that my issue was with the colon fencing in 57fcae1. I.e. if you try to add a new tab on the dev branch in Dynamic metadata after Regex, it splits it into a new group, but not with the tick fencing. Seems like a bug in one of the upstreams.

[henryiii]

Ahh, the outer blocks need more : than inner blocks. It works correctly if you use :::: for the tabs and ::: for the thing inside (and after), it works correctly.

[henryiii]

This doesn't affect the reworked docs in this PR, right?

[LecrisUT]

This doesn't affect the reworked docs in this PR, right?

😅 no those are long moved. Well except the versionchanged block, I've copied with the tick fencing from the 1st commit