def row_style(index, style, options={})
      offset = options.delete(:col_offset) || 0
      cells = cols[(offset..-1)].map { |column| column[index] }.flatten.compact
      cells.each { |cell| cell.style = style }
    end
Set the style for cells in a specific row
@param [Integer] index or range of indexes in the table
@param [Integer] style the cellXfs index
@param [Hash] options the options used when applying the style
@option [Integer] :col_offset only cells after this column will be updated.
@note You can also specify the style in the add_row call
@see Worksheet#add_row
@see README.md for an example