def [](row_index)
      if Fixnum === row_index
        rows[row_index]
      else
        ref = org.apache.poi.ss.util.CellReference.new(row_index)
        cell = rows[ref.row][ref.col]
        cell && cell.value ? cell.value : cell
      end
    end
def [](row_index)
      if Fixnum === row_index
        rows[row_index]
      else
        ref = org.apache.poi.ss.util.CellReference.new(row_index)
        cell = rows[ref.row][ref.col]
        cell && cell.value ? cell.value : cell
      end
    end
Accepts a Fixnum or a String as the row_index

 row_index as Fixnum: returns the 0-based row

 row_index as String: assumes a cell reference within this sheet
    if the value of the reference is non-nil the value is returned,
    otherwise the referenced cell is returned