Added button-press reporting, and eliminate rounding error if rate near 0.

This patch to hues.py adds rate reporting. Whenever a button is pressed, resulting in a rate change, the new rate is reported on screen.  Also, because of floating point rounding errors, the rate could become increasingly imprecise making it impossible to ever reach zero again.  Now when rate becomes very close to zero it is reset to precisely zero to eliminate rounding imprecision.