#93

update: libxlsxwriter 1.2.4 with upstream directory structure

Protect function definition (noted on rchk result)

Add xl_hyperlink_cell() to create hyperlinked cells (where the value is the direct cell content instead of the formula)

Escape double quotes

Freeze panes

Update to libxlsxwriter version 1.2.3

Minor housekeeping

Raise an error if column class is unsupported

typo 'columnn' -> 'column'