def [](i, *j)
      if i.is_a? String
        super(y(i),x(i))
      else
        super(i,j[0])
      end
    end
def [](i, *j)
      if i.is_a? String
        super(y(i),x(i))
      else
        super(i,j[0])
      end
    end
The [] method overrides the standard Matrix::[]. It will now accept Excel-style cell coordinates.
 @param [String] i
 @return [Cell] the object denoted with the Excel column-row name.
 @example Select a cell in a sheet
   w = Oxcelix::Workbook.new('Example.xlsx')
   w.sheets[0][3,1] #=> #<Oxcelix::Cell:0x00000001e00fa0 @xlcoords="B4", @style="0", @type="n", @value="3">
   w.sheets[0]['B4'] #=> #<Oxcelix::Cell:0x00000001e00fa0 @xlcoords="B4", @style="0", @type="n", @value="3">