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/fftshift.m
+++ b/scripts/signal/fftshift.m
@@ -19,12 +19,12 @@
 ## -*- texinfo -*-
 ## @deftypefn  {Function File} {} fftshift (@var{x})
 ## @deftypefnx {Function File} {} fftshift (@var{x}, @var{dim})
-## Perform a shift of the vector @var{x}, for use with the @code{fft}
-## and @code{ifft} functions, in order the move the frequency 0 to the
-## center of the vector or matrix.
+## Perform a shift of the vector @var{x}, for use with the @code{fft} and
+## @code{ifft} functions, in order the move the frequency 0 to the center of
+## the vector or matrix.
 ##
-## If @var{x} is a vector of @math{N} elements corresponding to @math{N}
-## time samples spaced by @nospell{@math{dt}}, then
+## If @var{x} is a vector of @math{N} elements corresponding to @math{N} time
+## samples spaced by @nospell{@math{dt}}, then
 ## @code{fftshift (fft (@var{x}))} corresponds to frequencies
 ##
 ## @example
@@ -34,11 +34,12 @@
 ## @noindent
 ## where @nospell{@math{df} = 1 / @math{dt}}.
 ##
-## If @var{x} is a matrix, the same holds for rows and columns.  If
-## @var{x} is an array, then the same holds along each dimension.
+## If @var{x} is a matrix, the same holds for rows and columns.  If @var{x}
+## is an array, then the same holds along each dimension.
 ##
-## The optional @var{dim} argument can be used to limit the dimension
-## along which the permutation occurs.
+## The optional @var{dim} argument can be used to limit the dimension along
+## which the permutation occurs.
+## @seealso{ifftshift}
 ## @end deftypefn
 
 ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp>