def find_field name
      return field[name] if field[name]
      @lines.each do | line |
        value = line.scan(/###{name}=(.*)/)
        if value[0]
          v = value[0][0]
          field[name] = v
          return v
        end
      end
      nil
    end
def find_field name
      return field[name] if field[name]
      @lines.each do | line |
        value = line.scan(/###{name}=(.*)/)
        if value[0]
          v = value[0][0]
          field[name] = v
          return v
        end
      end
      nil
    end
Look for a line in the header with the field name and return the
 value, otherwise return nil