doc: Update more docstrings to have one sentence summary as first line. Reviewed optimization, polynomial, signal script directories. * scripts/optimization/fminbnd.m, scripts/optimization/fminsearch.m, scripts/optimization/fminunc.m, scripts/optimization/fsolve.m, scripts/optimization/fzero.m, scripts/optimization/glpk.m, scripts/optimization/lsqnonneg.m, scripts/optimization/pqpnonneg.m, scripts/optimization/qp.m, scripts/optimization/sqp.m, scripts/polynomial/compan.m, scripts/polynomial/mkpp.m, scripts/polynomial/mpoles.m, scripts/polynomial/pchip.m, scripts/polynomial/poly.m, scripts/polynomial/polyaffine.m, scripts/polynomial/polyder.m, scripts/polynomial/polyeig.m, scripts/polynomial/polyfit.m, scripts/polynomial/polygcd.m, scripts/polynomial/polyint.m, scripts/polynomial/polyout.m, scripts/polynomial/polyval.m, scripts/polynomial/ppder.m, scripts/polynomial/ppint.m, scripts/polynomial/ppjumps.m, scripts/polynomial/ppval.m, scripts/polynomial/residue.m, scripts/polynomial/roots.m, scripts/polynomial/spline.m, scripts/polynomial/splinefit.m, scripts/polynomial/unmkpp.m, scripts/signal/arch_fit.m, scripts/signal/arch_rnd.m, scripts/signal/arma_rnd.m, scripts/signal/autoreg_matrix.m, scripts/signal/bartlett.m, scripts/signal/blackman.m, scripts/signal/detrend.m, scripts/signal/diffpara.m, scripts/signal/durbinlevinson.m, scripts/signal/fftconv.m, scripts/signal/fftfilt.m, scripts/signal/fftshift.m, scripts/signal/filter2.m, scripts/signal/freqz.m, scripts/signal/hamming.m, scripts/signal/hanning.m, scripts/signal/hurst.m, scripts/signal/ifftshift.m, scripts/signal/periodogram.m, scripts/signal/sinc.m, scripts/signal/sinetone.m, scripts/signal/sinewave.m, scripts/signal/spectral_adf.m, scripts/signal/spectral_xdf.m, scripts/signal/spencer.m, scripts/signal/stft.m, scripts/signal/synthesis.m, scripts/signal/unwrap.m, scripts/signal/yulewalker.m: Update more docstrings to have one sentence summary as first line.

--- a/scripts/signal/diffpara.m
+++ b/scripts/signal/diffpara.m
@@ -23,14 +23,15 @@
 ##
 ## The frequencies from @math{[2*pi*a/t, 2*pi*b/T]} are used for the
 ## estimation.  If @var{b} is omitted, the interval
-## @math{[2*pi/T, 2*pi*a/T]} is used.  If both @var{b} and @var{a} are
-## omitted then @math{a = 0.5 * sqrt (T)} and @math{b = 1.5 * sqrt (T)}
-## is used, where @math{T} is the sample size.  If @var{x} is a matrix,
-## the differencing parameter of each column is estimated.
+## @math{[2*pi/T, 2*pi*a/T]} is used.  If both @var{b} and @var{a} are omitted
+## then @math{a = 0.5 * sqrt (T)} and @math{b = 1.5 * sqrt (T)} is used, where
+## @math{T} is the sample size.  If @var{x} is a matrix, the differencing
+## parameter of each column is estimated.
 ##
-## The estimators for all frequencies in the intervals
-## described above is returned in @var{dd}.  The value of @var{d} is
-## simply the mean of @var{dd}.
+## The estimators for all frequencies in the intervals described above is
+## returned in @var{dd}.
+##
+## The value of @var{d} is simply the mean of @var{dd}.
 ##
 ## Reference: @nospell{P.J. Brockwell & R.A. Davis}. @cite{Time Series:
 ## Theory and Methods}. Springer 1987.