Clock out an initial word to the TLCs. This seems to help get stable
initialisation.

My guess is that the very first clock edge gets ill-defined without this,
causing the first bit to be possibly corrupted.

Also add some basic re-try mechanism (but it doesn't seem to be needed
anymore).
Add FAKE_HALL_SENSOR preprocessor macro.

This macro is useful for testing; it makes the code ignore the hall sensor,
and instead simulate a specific rate of rotation. This allows to test the code
without actually setting the hardware spinning.