Reworked to use i2c_t3 library for i2c, which supports
both of the i2c buses on the Teensy 3. The sketch in this
commit expects the Nunchuck to be hooked up to the second
i2c bus (SDA = pin 17, SCL pin 16). No special reason, other
than I wanted to verify that a Nunchuck connected to the
second bus would work, and I didn't bother to go back to
having the Nunchuck on the first bus.