The sketch in a nut shell

The developing of the sketch has been finished few days ago and can now be considered pretty much complete, so I guess it's time for a review.

The sketch.ino file is an easy 200 lines C++ source code that is supposed to work as a slave. Main purposes are:

• read the current values of the sensors and provide them to the upper layer;
• read the current values of the outputs and provide them to the upper layer;
• get, from the upper layer, the expected status of the outputs and operate to address the request.