def table= table
      raise(ArgumentError, "value should be nil or Workbook::Table") unless [NilClass,Workbook::Table].include? table.class
      @table = table
    end
def table= table
      raise(ArgumentError, "value should be nil or Workbook::Table") unless [NilClass,Workbook::Table].include? table.class
      @table = table
    end
Set the table this column belongs to
 @param [Workbook::Table] table this column belongs to