Our documentation pages are getting increasingly long in the
ikiwiki. So I sometimes need to link to specific sections. For
example, this link:

https://help.torproject.org/tsa/howto/ganeti/#index4h2

... currently points at "Adding a new instance". Yet there are a few
problems with that link:

 1. it's not human-readable: it's hard to understand what it refers to
    just by looking at it
 2. it's not stable: if another heading is added or remove before it,
    its number is going to change and the link will point elsewhere

There's a plugin called [headinganchors] which adds better
identifiers, but it has some limitations with non-ASCII characters. I
wrote a [replacement plugin][i18nheadinganchors] but it's not shipped
in ikiwiki by default.

 [headinganchors]: https://ikiwiki.info/plugins/headinganchors/
 [i18nheadinganchors]: https://ikiwiki.info/plugins/contrib/i18nheadinganchors/

This enables the former to see how it looks.

We don't *have* a CGI interface, as far as I know. So this is pointless.

This will make future module diffs easier to read. Should be a noop.