doc: Update more docstrings to have one sentence summary as first line. Reviewed specfun, special-matrix, testfun, and time script directories. * scripts/specfun/expint.m, scripts/specfun/isprime.m, scripts/specfun/legendre.m, scripts/specfun/primes.m, scripts/specfun/reallog.m, scripts/specfun/realsqrt.m, scripts/special-matrix/gallery.m, scripts/special-matrix/hadamard.m, scripts/special-matrix/hankel.m, scripts/special-matrix/hilb.m, scripts/special-matrix/invhilb.m, scripts/special-matrix/magic.m, scripts/special-matrix/pascal.m, scripts/special-matrix/rosser.m, scripts/special-matrix/toeplitz.m, scripts/special-matrix/vander.m, scripts/special-matrix/wilkinson.m, scripts/testfun/assert.m, scripts/testfun/demo.m, scripts/testfun/example.m, scripts/testfun/fail.m, scripts/testfun/rundemos.m, scripts/testfun/runtests.m, scripts/testfun/speed.m, scripts/time/asctime.m, scripts/time/calendar.m, scripts/time/clock.m, scripts/time/ctime.m, scripts/time/datenum.m, scripts/time/datestr.m, scripts/time/datevec.m, scripts/time/etime.m, scripts/time/is_leap_year.m, scripts/time/now.m, scripts/time/weekday.m: Update more docstrings to have one sentence summary as first line.

--- a/scripts/time/etime.m	Sun May 03 15:36:23 2015 -0700
+++ b/scripts/time/etime.m	Sun May 03 17:00:11 2015 -0700
@@ -19,7 +19,9 @@
 ## -*- texinfo -*-
 ## @deftypefn {Function File} {} etime (@var{t2}, @var{t1})
 ## Return the difference in seconds between two time values returned from
-## @code{clock} (@math{@var{t2} - @var{t1}}).  For example:
+## @code{clock} (@math{@var{t2} - @var{t1}}).
+##
+## For example:
 ##
 ## @example
 ## @group
@@ -30,8 +32,8 @@
 ## @end example
 ##
 ## @noindent
-## will set the variable @code{elapsed_time} to the number of seconds since
-## the variable @code{t0} was set.
+## will set the variable @code{elapsed_time} to the number of seconds since the
+## variable @code{t0} was set.
 ## @seealso{tic, toc, clock, cputime, addtodate}
 ## @end deftypefn