Log Message:
textproc/libxlsxwriter: Update to 0.9.9

Changes in 0.9.6:
 - Added support for chart custom data labels.
 - Fix for issue where array formulas weren't included in the output
   file for certain ranges/conditions. Issue #735.

Changes in 0.9.7:
 - Changed #lxw_chart_data_label field from .delete to .hide in order to
   avoid reserved word conflict with C++. Issue #300

Changes in 0.9.8:
 - Added formatting for chart data labels and chart custom data labels.

Changes in 0.9.9:
 - Added support for images in headers and footers. See
   worksheet_set_header_opt().
 - Added worksheet_ignore_errors() function to ignore Excel worksheet
   errors/warnings in user defined ranges.