sheet_to_json
uses `defval` key in options object fixes #583 h/t @jimjin fixes #582 h/t @jimjin fixes #147 h/t @jtadmor
- sheet_to_csv strip option (fixes #182 h/t @davidworkman9) - sheet_to_json dateNF option (fixes #134 h/t @rotemtam) - file type detection expanded to 4 byte magic number
- multiformat column widths (fixes #591 h/t @sheeeeep) - skip nested BIFF files