add audio_degrader

[faroit]

https://github.com/emilio-molina/audio_degrader

[sevagh]

Can I suggest my alternative instead: https://github.com/sevagh/audio-degradation-toolbox

[faroit]

how do they differ?

[sevagh]

Hmm, I believed I had implemented more of the original MATLAB code, but seeing as this one is more maintained (and also precedes mine - I based mine on emilio-molina's original), the original is better.

Mine has some limitations and I wrote it too long ago for it to matter anymore.