Compensate frequency warping

[TexZK]

See: https://en.wikipedia.org/wiki/Bilinear_transform#Frequency_warping
Where:

2/T ← w0 / tan( w0*T/2 )

For example, within coefficient calculations, where:

2/T ← 1/k = 2*fs

replace:

k = 0.5 * fs ← k = tan( w0*0.5/fs ) / w0