GitLab

* Add basic low pass filtering
* Add highpass filtering
* More tests of IIR vs FIR
* Implement convolve function, add tests
* Move lfilter and convolve into functional, more tests
* added additional documentation for convolve and lfilter, renamed functional_filtering to functional_sox_convenience
* Follow naming convention for sample rate in functional
* fix failing vctk manifest test to account for adding more test audios into assets
* Adding documentation for lfilter, biquad, highpass_biquad, lowpass_biquad
* added matrix based implementation of lfilter
* adding python lfilter implementation
* factor out biquad, lowpass, highpass to sox compatibility