Wrap author attributions in <sect1info> and <sect2info> as
appropriate.

I've specifically left JKH's attribution for the "FreeBSD History"
section in tact, since this is a first person account of the history
of FreeBSD and as such the author needs to be identified in place.
This could probably be marked up differently, but its clear that this
section is different from all of the other "contributed by XXX" in the
Handbook.

Also add support for <sect1info> and <sect2info> to the stylsheet so
that these attributions get displayed as they have been.