Arduino: Analog input

[mitra42]

See #63 for some references and pointers

• Find analog input pins on both Arduino and ESP8266
• Modify sketch to get back constants for things like A0 nad esp8266:D4 see https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/
• Write Forth words for analogRead
• Build hardware test scenario (Pot as input ?) and test