sandbox/iirfilt_intdiff: deriving coefficients from zeros/poles
sandbox/iirfilt_intdiff: deriving coefficients from zeros/poles

  * digital gain was computed emperically
  * need to find more appropriate way of determining gain
  * composite transfer function of integrate+differentiate not flat

wangning223/liquid-dsp,wangning223/liquid-dsp,biotrump/liquid-dsp,jgaeddert/liquid-dsp,andrepuschmann/liquid-dsp,biotrump/liquid-dsp,manuts/liquid-dsp,jgaeddert/liquid-dsp,jgaeddert/liquid-dsp,JayKickliter/liquid-dsp,manuts/liquid-dsp,JayKickliter/liquid-dsp,manuts/liquid-dsp,andrepuschmann/liquid-dsp,cjcliffe/liquid-dsp,manuts/liquid-dsp,JayKickliter/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,andrepuschmann/liquid-dsp,jgaeddert/liquid-dsp,wangning223/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,biotrump/liquid-dsp,cjcliffe/liquid-dsp,biotrump/liquid-dsp,wangning223/liquid-dsp,cjcliffe/liquid-dsp,JayKickliter/liquid-dsp,manuts/liquid-dsp,JayKickliter/liquid-dsp,jgaeddert/liquid-dsp,cjcliffe/liquid-dsp,biotrump/liquid-dsp