various other constants need to scale according to POLLING_RATE.
DEBOUNCE_TC ends up pretty small with small POLLING_RATEs, but there's
nothing to be done about that.
.. tested (but not committed) with 60, so that (in principle) I can poll
during the vertical retrace interval while generating a TV signal.
Allow commandline selection of polarity, jitter, timebase, noise,
and phase. This makes it easy to demonstrate what signal variations
the receiver will tolerate.
Make it run faster by using numpy to add noise, instead of dealing with
each character of output separately.
What we desire is long-term stability at the expense of short-term
accuracy. Therefore, don't steer the timer based on local measurements
(which has a very low precision, counts per wwvb second is 1/1000
or 1000ppm), but instead base it on long-term measurements (e.g., counts
per wwvb day or so, 12ppb)
The resolution of the divisor is 1 clock per 32.678 seconds, or 6ppb when
the clock is nominally 5MHz.
