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.

FCN_FILE_DIRS += testfun

testfun_FCN_FILES = \
  testfun/__have_feature__.m \
  testfun/__printf_assert__.m \
  testfun/__prog_output_assert__.m \
  testfun/__run_test_suite__.m \
  testfun/assert.m \
  testfun/demo.m \
  testfun/example.m \
  testfun/fail.m \
  testfun/rundemos.m \
  testfun/runtests.m \
  testfun/speed.m \
  testfun/test.m

FCN_FILES += $(testfun_FCN_FILES)

PKG_ADD_FILES += testfun/PKG_ADD

DIRSTAMP_FILES += testfun/$(octave_dirstamp)