Split output by chapters. The index is still basic, just "Section N"
entries so far.

Change-Id: I4db659ee4110ab30f4b75f44c41f958533ddad7f
Reviewed-on: https://gerrit.libreoffice.org/41177Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>