Harmonic Product Spectrum Changes

Rewrote the xtract_hps function. It seems to work a lot better now.

I changed the interface a little, *data is now a pointer to the whole of *result from xtract_spectrum (including the frequency data). And you no longer need to pass in the sample rate.

I also added a little fix to xtract_irregularity_j as i suggested in the last issue I raised.