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/sub2ind.cc	Thu May 07 17:16:36 2015 -0400
+++ b/libinterp/corefcn/sub2ind.cc	Sat May 09 17:19:30 2015 -0700
@@ -69,10 +69,9 @@
 @deftypefnx {Function File} {@var{ind} =} sub2ind (@var{dims}, @var{s1}, @var{s2}, @dots{}, @var{sN})\n\
 Convert subscripts to a linear index.\n\
 \n\
-The following example shows how to convert the two-dimensional\n\
-index @code{(2,3)} of a 3-by-3 matrix to a linear index.  The matrix\n\
-is linearly indexed moving from one column to next, filling up\n\
-all rows in each column.\n\
+The following example shows how to convert the two-dimensional index\n\
+@code{(2,3)} of a 3-by-3 matrix to a linear index.  The matrix is linearly\n\
+indexed moving from one column to next, filling up all rows in each column.\n\
 \n\
 @example\n\
 @group\n\