The 'All Posts' link used to overlap with the table of contents at the end of a post. This occured because the ToC is sticky to the `main` block, so it scrolled up before the `comments` section. The 'All Post' link, however, is fixed, so it does not scroll up.
This commit fixes the issue by moving the comment block to the main block (from the after_main block). This way, the ToC stays visible in the comment section. We also add the comment section to the ToC.
The <article> tag is for self-contained content, which the post list isn't really. I hope that this change makes search engines display the blog's introduction instead of the first post's introduction in their results.
This ToC is only shown when the screen is too small for the sticky sidebar ToC.
We use a `<!-- toc -->` comment and the `replace` function to allow inserting the ToC at well defined points of the page. We don't use the shortcode feature of Zola because of https://github.com/getzola/zola/issues/584.
