Log Message:
textproc/libxlsxwriter: Update to 0.8.8

Changes:
 - Added option to allow a user defined, or overridden, image
   description used with `worksheet_insert_image()`. By default it uses
   the filename as the description.
 - Added Windows portable version of `fopen` to handle utf8 filenames
   when working with images.
 - Added an option to allow chart fonts to be rotation to 270 deg to
   give a stacked orientation. Also added support for East Asian
   vertical chart fonts.
 - Refactored struct types used in pubic APIs to remove or document
   hidden fields.

   NOTE: This change introduces backward incompatible API changes.
   However, it should minimize any future changes of this nature.