While the HTML standard allows multiple <h1> elements in the same

While the HTML standard allows multiple <h1> elements in the same
document, <h1> is intended for top level headers, and most of the
sections in a manual page can hardly be considered top-level.
It is more usual to use <h1> only for the main title of the document
of for the site name.

Consequently, move .Sh/.SH from <h1> to <h2> and .Ss/.SS from <h2>
to <h3>, freeing <h1> for use by header.html in man.cgi(8).

Discussed with Anna Vyalkova <cyber at sysrq dot in>.