Peaking / Notch IIR Filter

Generates coefficients for a 2nd order IIR digital filter

Derive coefficients for a peaking filter with a given amplitude and bandwidth. All coefficients are calculated as described in Zolzer's
DAFX book (p. 50 - 55). This algorithm assumes a constant Q-term
is used through the equation.

Usage: [B,A] = peaking(G, Fc, Q, Fs);

G is the logrithmic gain (in dB)
FC is the center frequency
Q is Q-term equating to (Fb / Fc)
Fs is the sampling rate

The typical usages is multi-band equalization where each band has it's own peaking filter.