[Feature] Filtering for IIR and FIR

[spectre-ns]

This feature accepts a signal with a rational expression for the filter coefficients used to filter the signal where b is the numerator and a is the denominator or 'characteristic polynomial' of the digital filter being applied. Filtering is often accomplished using cascading second order sections to reduce numeral sensitivity.

https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.lfilter.html

[spectre-ns]

https://en.wikipedia.org/wiki/Digital_biquad_filter This is a good theoretical basis on the implemention.