add frm_def2empty, frm_dataset2xls

Signed-off-by: Mark Histed <mhisted@gmail.com>
xlswritepoi: work around a bug in POI with setting a numeric value in blank cells

Signed-off-by: Mark Histed <mhisted@gmail.com>
add some dataset funs and build in some type knowledge when writing/updating datasets

Signed-off-by: Mark Histed <mhisted@gmail.com>