doc: Update more docstrings to have one sentence summary as first line. Reviewed libinterp/corefcn directory. * libinterp/corefcn/__ilu__.cc, libinterp/corefcn/balance.cc, libinterp/corefcn/besselj.cc, libinterp/corefcn/betainc.cc, libinterp/corefcn/bitfcns.cc, libinterp/corefcn/bsxfun.cc, libinterp/corefcn/cellfun.cc, libinterp/corefcn/colloc.cc, libinterp/corefcn/conv2.cc, libinterp/corefcn/data.cc, libinterp/corefcn/debug.cc, libinterp/corefcn/defaults.cc, libinterp/corefcn/det.cc, libinterp/corefcn/dirfns.cc, libinterp/corefcn/dlmread.cc, libinterp/corefcn/dot.cc, libinterp/corefcn/eig.cc, libinterp/corefcn/error.cc, libinterp/corefcn/fft2.cc, libinterp/corefcn/fftn.cc, libinterp/corefcn/file-io.cc, libinterp/corefcn/filter.cc, libinterp/corefcn/find.cc, libinterp/corefcn/gammainc.cc, libinterp/corefcn/gcd.cc, libinterp/corefcn/getgrent.cc, libinterp/corefcn/getpwent.cc, libinterp/corefcn/getrusage.cc, libinterp/corefcn/graphics.cc, libinterp/corefcn/help.cc, libinterp/corefcn/hex2num.cc, libinterp/corefcn/input.cc, libinterp/corefcn/inv.cc, libinterp/corefcn/kron.cc, libinterp/corefcn/load-path.cc, libinterp/corefcn/load-save.cc, libinterp/corefcn/lookup.cc, libinterp/corefcn/ls-oct-ascii.cc, libinterp/corefcn/lsode.cc, libinterp/corefcn/lu.cc, libinterp/corefcn/luinc.cc, libinterp/corefcn/mappers.cc, libinterp/corefcn/matrix_type.cc, libinterp/corefcn/max.cc, libinterp/corefcn/md5sum.cc, libinterp/corefcn/mgorth.cc, libinterp/corefcn/nproc.cc, libinterp/corefcn/oct-hist.cc, libinterp/corefcn/ordschur.cc, libinterp/corefcn/pager.cc, libinterp/corefcn/pinv.cc, libinterp/corefcn/pr-output.cc, libinterp/corefcn/pt-jit.cc, libinterp/corefcn/quad.cc, libinterp/corefcn/quadcc.cc, libinterp/corefcn/qz.cc, libinterp/corefcn/rand.cc, libinterp/corefcn/rcond.cc, libinterp/corefcn/regexp.cc, libinterp/corefcn/schur.cc, libinterp/corefcn/sighandlers.cc, libinterp/corefcn/sparse.cc, libinterp/corefcn/spparms.cc, libinterp/corefcn/str2double.cc, libinterp/corefcn/strfind.cc, libinterp/corefcn/strfns.cc, libinterp/corefcn/sub2ind.cc, libinterp/corefcn/svd.cc, libinterp/corefcn/symtab.cc, libinterp/corefcn/syscalls.cc, libinterp/corefcn/sysdep.cc, libinterp/corefcn/time.cc, libinterp/corefcn/toplev.cc, libinterp/corefcn/tril.cc, libinterp/corefcn/tsearch.cc, libinterp/corefcn/typecast.cc, libinterp/corefcn/urlwrite.cc, libinterp/corefcn/utils.cc, libinterp/corefcn/variables.cc, scripts/polynomial/spline.m: Update more docstrings to have one sentence summary as first line.

--- a/libinterp/corefcn/conv2.cc
+++ b/libinterp/corefcn/conv2.cc
@@ -39,9 +39,10 @@
 @deftypefn  {Built-in Function} {} conv2 (@var{A}, @var{B})\n\
 @deftypefnx {Built-in Function} {} conv2 (@var{v1}, @var{v2}, @var{m})\n\
 @deftypefnx {Built-in Function} {} conv2 (@dots{}, @var{shape})\n\
-Return the 2-D convolution of @var{A} and @var{B}.  The size of the result\n\
-is determined by the optional @var{shape} argument which takes the following\n\
-values\n\
+Return the 2-D convolution of @var{A} and @var{B}.\n\
+\n\
+The size of the result is determined by the optional @var{shape} argument\n\
+which takes the following values\n\
 \n\
 @table @asis\n\
 @item @var{shape} = @qcode{\"full\"}\n\
@@ -294,9 +295,10 @@
        "-*- texinfo -*-\n\
 @deftypefn  {Built-in Function} {@var{C} =} convn (@var{A}, @var{B})\n\
 @deftypefnx {Built-in Function} {@var{C} =} convn (@var{A}, @var{B}, @var{shape})\n\
-Return the n-D convolution of @var{A} and @var{B}.  The size of the result\n\
-is determined by the optional @var{shape} argument which takes the following\n\
-values\n\
+Return the n-D convolution of @var{A} and @var{B}.\n\
+\n\
+The size of the result is determined by the optional @var{shape} argument\n\
+which takes the following values\n\
 \n\
 @table @asis\n\
 @item @var{shape} = @qcode{\"full\"}\n\