Fix overlap of 'All Posts' and ToC; add comments to ToC

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.

blog/templates/macros.html

@@ -43,6 +43,7 @@
                     </li>{% endfor %}
                 </ul>{% endif %}
             </li>{% endfor %}
+            <li class="toc-comments-link"><a href="#comments">Comments</a></li>
         </ul>
     </details>
 {% endmacro toc %}