Added testing for random input and PSD

So the previous testing scripts biquad_psd_test_1 and 2 did a couple
things wrong. First they didn't reset the filters back to zero state.
Second, the idea of a frequency sweep doesn't make a lot of intuitive
sense, so the data is really meaningless. Biquad test #3 just inputs
random data at different frequencies and then looks at the difference
(the Q noise) and plots the power spectral density of that which makes
more sense. The Q should have the same spectrum regardless of the input,
so the input should be a random input, not a series of frequencies. The
next commit will have a larger data set for the final presentation.