texinfo: Update to version 6.8

texinfo: Update to version 6.8

- Update from 6.7 to 6.8
- Update rootfile
- Changelog is too large to include here. Full details can be found in the
   ChangeLog file in the source tarball
   Following is the content of the NEWS file from the source tarball which highlights
    noteworthy changes, very tersely.
   6.8 (3 July 2021)
    * Language
      . new command @displaymath for formatting of mathematical notation
      . @example takes an argument to specify the language
      . mark these commands as deprecated, not to be used:
        @centerchap, @definfoenclose, @refill, @inforef.
      . new paper size @bsixpaper
    * texi2any
      . should be faster as Perl XS parser is enabled by default
      . SHOW_MENU customization variable replaced by FORMAT_MENU.
        FORMAT_MENU set to 'menu' is the same as SHOW_MENU set to 1, and
        FORMAT_MENU set to 'nomenu' is the same as SHOW_MENU set to 0.
      . only check menu structure if CHECK_NORMAL_MENU_STRUCTURE variable is set
      . changes to HTML output:
          . MathJax support for display of math.  new variables HTML_MATH,
            MATHJAX_SCRIPT and MATHJAX_SOURCE.
          . new variables JS_WEBLABELS and JS_WEBLABELS_FILE to support
            JavaScript License Web Labels
          . by default, use sectional tables of contents instead of menus
          . use section names in links by default (configure with
            xrefautomaticsectiontitle customization variable)
          . CONTENTS_OUTPUT_LOCATION sets location of table of contents
          . document sections wrapped in <div> elements
          . new variable USE_NODE_DIRECTIONS to use node or section structure
            for node directions
          . copiable anchor links for definitions with COPIABLE_ANCHORS variable
          . experimental JavaScript browsing interface enabled with INFO_JS_DIR
          . don't add an extra period before file extension given as an argument
            to @image if image file is not found
    * info
      . support compressed dir files
    * texi2dvi
      . stop on first error in input file
    * texinfo.tex
      . put logical page numbers into PDF's ('page labels')
      . put chapter numbers in the PDF outline
      . new Finnish translation
    * Distribution
      . autoconf 2.71, automake 1.16.3, gettext 0.21

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>