gawk html documentation - h4 and h5 closes h3 tags

[Andresen, Kai]

There is a tiny bug in the gawk html documentation (both single and multiple 
file versions).

The err is that a lot of subsection (and subsubsection) headings have 
inconsistent header-tags (opening and closing tags are different levels):

<h3 class="subsubheading">Dark Corners</h5>
--^
-----------------------------------------^


It was easy to fix with a regex, but I guess all these, and possibly some other 
GNU documentation, are generated using some tool that needs fixing?

Kind regards, and thanks for great tools!
Kai