Some optimizations

* Use INT1 instead of change notification to get a quicker
  handling of the interrupt.
* INT1 has highest priority in order to avoid problems when
  using Bluetooth
* Don't shift around the bits, change the mask definition
  instead.
* Remove LEFT things since we managed with one shift register
* Disable debug printing.
* Write directly to latch register instead of using
  SetDigitalOutLevel.