Lint markdown; fix version and footnote; add examples

[tohn]

I used markdownlint, but ignored MD033 and MD013 in the code lines.

Furthermore I fixed the version for type/section specific hooks and removed the footnote (since it's possible now).

And to complete the changes in Version 0.73.0, I added the blog example in the directory tree together with render-heading.html.

[bep]

So, the "max n chars per line" is something I would never do myself when writing Markdown, so we cannot have a linter that somehow complains about that.

[tohn]

So, the "max n chars per line" is something I would never do myself when writing Markdown, so we cannot have a linter that somehow complains about that.

Ok. So should I revert the "max n chars per line" changes? Or is it fine for now, but should be excluded as proposed by #1102 (I saw this after I created this PR)?

[bep]

Let us conclude with #1102 before we start linting.

[tohn]

Let us conclude with #1102 before we start linting.

Sounds good. I reverted the markdownlint changes.

[coliff]

hey @bep - the linting changes have been reverted, so is the content for this PR ok to be merged?

[tohn]

Hello, any news on this?

[jmooring]

This has been obsolete for a while. The render hook documentation has been moved and revised several times.