Initial release of code for the Engduino v2.1

This is a release of code for the Engduino version 2.1. It is not
compatible with the Engduino v1.0, largely because there was a redesign
of the electronics meaning that (i) sensors are connected to different
pins on the microprocessor; (ii) there are more sensors; and (iii) the
LEDs are numbered from 0-15 rather than 1-16