A binary full-adder that takes into the state of three binary inputs (0, 1) and returns the result in the state of the two LEDs.
An output of 1 means 1 of the 3 inputs is a 1.
An output of 2 means 1 bit is added to another bit to get a total of 2.
An output of 3 means there's a carry over (if there was another bit full adder after this one).
