I am glad that you fixed the issue with missing the
Keyboard.h library in the PrimeDemo example code; thank you for letting us know.
As for your second issue, you contacted us directly about this as well, and I already responded, but I wanted to post the answer here for others to see as well.
buttonMonitor is a function in the "Demo" example sketch, which is located near the bottom. I was able to reproduce the problem using Arduino 1.6.6. It looks like there might be a bug with that version where function prototypes in the sketch are not always properly generated. For now, you can work around the issue by adding the function prototype yourself. Just add this line near the top of the sketch: