add way to skip toc entries

doc/todo/allow_toc_to_skip_entries.mdwn

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+[[!template  id=gitbranch branch=anarcat/toc-skip author="[[anarcat]]"]]
+
+a long-standing irritationf the [[plugins/toc]] plugin is that it counts *all* headings in the document. since it's frequently the case that themes will use the first H1 to show a title (and that there's no way to "bump" the level of headings generated by the markup), you often end up with a table of contents that looks like this:
+
+ * TITLE
+ * Heading 1
+   * Subheading 1
+ * Heading 2
+
+... even though the content is actually something like:
+
+    # Heading 1
+    ## Subheading 2
+    # Heading 2
+
+That's a bit confusing. I would expect the table of contents to only have:
+
+ * Heading 1
+   * Subheading 1
+ * Heading 2
+
+... and somehow ignore my title.
+
+That is hard to fix without changing the theme significantly. ikiwiki themes frequently workaround that problem by showing the title using another markup element, generally a `<span>`. But I find that confusing as well, because `<span>` is a generic, non-semantic element, which, even worse, is by default not a "block" like a heading. In bootstrap, for example, you would need to copy all the logic surrounding headings to a theme customization to make it work, but that leads to a lot of CSS duplication.
+
+There should really be a way to skip those entries. The patch mentioned here does this by doing a tiny modification to `toc.pm` to skip headings with the magic `nocount` class. The naming comes from [Phil Archer's Automatic Heading Numbering CSS hack](https://philarcher.org/diary/2013/headingnumbers) and could be changed, but it seemed logical to me. The result can be seen in action in: <https://anarc.at/blog/2019-11-20-file-monitoring-tools/>.
+
+Thank you for your consideration.