Add Extended Analog about pyfirmata HOT 2 OPEN

  # use the extended analog feature if the pin no. >15
  # this will allow PWM and SERVO on all possible pins,
  # for teensy boards for example. 
  # Keep the old message format for pins <=15 for
  # compatibility with older firmata versions.

        if self.pin_number < 16:
            msg = chr(ANALOG_MESSAGE + self.pin_number)
            msg += chr(value % 128)
            msg += chr(value >> 7)
            self.board.sp.write(msg)
        else:
            msg = chr(self.pin_number)
            msg += chr(value % 128)
            msg += chr(value >> 7)
            self.board.send_sysex(EXTENDED_ANALOG, msg)

        if self.pin_number < 16:
            msg = chr(ANALOG_MESSAGE + self.pin_number)
            msg += chr(value % 128)
            msg += chr(value >> 7)
            self.board.sp.write(msg)
        else:
            msg = chr(self.pin_number)
            msg += chr(value % 128)
            msg += chr(value >> 7)
            self.board.send_sysex(EXTENDED_ANALOG, msg)