3 or 4 days of fiddling with PLL compressed down into a single small commit:
3 or 4 days of fiddling with PLL compressed down into a single
small commit:

o Compensate for a peculiar shape of the phase detector output
  which goes from 1.5 to 0.5 when the control loop goes from 0% to 100%
  CPU utilization and then jumps to -0.5 and goes down
  (to minus infinity?) as it takes longer and longer to execute.

o Add spurious error supression using erf() function and
  comparing new phase detector output value with the last filtered
  value.

o Add proper error amplification to ensure proper load regulation
  within operating range of CPU usage.

o Add some extra debug code, ifdefed out.

sobomax/libelperiodic,sobomax/libelperiodic,sobomax/libelperiodic,sobomax/libelperiodic