doc: Update more docstrings to have one sentence summary as first line. Reviewed build-aux, libinterp/dldfcn, libinterp/octave-value, libinterp/parse-tree directories. * build-aux/mk-opts.pl, libinterp/dldfcn/__magick_read__.cc, libinterp/dldfcn/amd.cc, libinterp/dldfcn/audiodevinfo.cc, libinterp/dldfcn/audioread.cc, libinterp/dldfcn/ccolamd.cc, libinterp/dldfcn/chol.cc, libinterp/dldfcn/colamd.cc, libinterp/dldfcn/convhulln.cc, libinterp/dldfcn/dmperm.cc, libinterp/dldfcn/fftw.cc, libinterp/dldfcn/qr.cc, libinterp/dldfcn/symbfact.cc, libinterp/dldfcn/symrcm.cc, libinterp/octave-value/ov-base.cc, libinterp/octave-value/ov-bool-mat.cc, libinterp/octave-value/ov-cell.cc, libinterp/octave-value/ov-class.cc, libinterp/octave-value/ov-fcn-handle.cc, libinterp/octave-value/ov-fcn-inline.cc, libinterp/octave-value/ov-java.cc, libinterp/octave-value/ov-null-mat.cc, libinterp/octave-value/ov-oncleanup.cc, libinterp/octave-value/ov-range.cc, libinterp/octave-value/ov-struct.cc, libinterp/octave-value/ov-typeinfo.cc, libinterp/octave-value/ov-usr-fcn.cc, libinterp/octave-value/ov.cc, libinterp/parse-tree/lex.ll, libinterp/parse-tree/oct-parse.in.yy, libinterp/parse-tree/pt-binop.cc, libinterp/parse-tree/pt-eval.cc, libinterp/parse-tree/pt-mat.cc: doc: Update more docstrings to have one sentence summary as first line.

--- a/libinterp/parse-tree/pt-mat.cc
+++ b/libinterp/parse-tree/pt-mat.cc
@@ -1391,8 +1391,10 @@
 @deftypefnx {Built-in Function} {@var{old_val} =} string_fill_char (@var{new_val})\n\
 @deftypefnx {Built-in Function} {} string_fill_char (@var{new_val}, \"local\")\n\
 Query or set the internal variable used to pad all rows of a character\n\
-matrix to the same length; It must be a single character.  The default\n\
-value is @qcode{\" \"} (a single space).  For example:\n\
+matrix to the same length.\n\
+\n\
+The value must be a single character and the default is @qcode{\" \"} (a\n\
+single space).  For example:\n\
 \n\
 @example\n\
 @group\n\
@@ -1405,7 +1407,7 @@
 @end example\n\
 \n\
 When called from inside a function with the @qcode{\"local\"} option, the\n\
-variable is changed locally for the function and any subroutines it calls.  \n\
+variable is changed locally for the function and any subroutines it calls.\n\
 The original variable value is restored when exiting the function.\n\
 @end deftypefn")
 {