def add_format format
      if format.is_a? Workbook::Format
        if format.name
          @formats[format.name]=format
        else
          @formats[@formats.keys.count]=format
        end
      else
        raise ArgumentError, "format should be a Workboot::Format"
      end
    end
def add_format format
      if format.is_a? Workbook::Format
        if format.name
          @formats[format.name]=format
        else
          @formats[@formats.keys.count]=format
        end
      else
        raise ArgumentError, "format should be a Workboot::Format"
      end
    end
Add a Workbook::Format to the template
 @param [Workbook::Format] format (of a cell) to add to the template