def label(labelname)
      read_labels
      return [nil, nil, nil] if @label.size < 1 || !@label.key?(labelname)
      [
        @label[labelname][1].to_i,
        ::Roo::Utils.letter_to_number(@label[labelname][2]),
        @label[labelname][0]
      ]
    end
def label(labelname)
      read_labels
      return [nil, nil, nil] if @label.size < 1 || !@label.key?(labelname)
      [
        @label[labelname][1].to_i,
        ::Roo::Utils.letter_to_number(@label[labelname][2]),
        @label[labelname][0]
      ]
    end
returns the row,col values of the labelled cell
 (nil,nil) if label is not defined