Function xl::excel_number_to_date

pub fn excel_number_to_date(
    number: f64, 
    date_system: &DateSystem
) -> DateConversion

Return date of “number” based on the date system provided.

The date system is either the 1904 system or the 1900 system depending on which date system the spreadsheet is using. See http://bit.ly/2He5HoD for more information on date systems in Excel.