Add scipy.signal.iirdesign()

applications/lofar2/model/pfb_os/dsp_study_erko.txt

@@ -449,6 +449,7 @@
    . Optimized IIR design methods, iteratively adjust coefficients to achieve
      a specified arbitrary frequency response (f_pass, f_stop, r_pass_dB,
      r_stop_dB bands).
+     . scipy.signal.iirdesign(), can do all of:
        . scipy.signal.cheby2(), ripple in stop band
        . scipy.signal.cheby1(), ripple in pass band
        . scipy.signal.butter(), maximally flat in pass band, decay in stop band