Improve 2019/burton/try.sh + shellcheck comments

The shellcheck comments are in cow.sh and check.sh: added the URL for
each supposed problem as per that issue.

2019/burton/check.sh

@@ -16,8 +16,11 @@ echo | $x
 /bin/echo -n a | $x
 echo a | $x
 $x < newlines
-# ^---^ SC2210 (warning): This is a file redirection. Was it supposed to be a comparison or fd operation?
-# Answer: 256 is a file so it is supposed to be file redirection.
+# 256 is a file so it is supposed to be file redirection. Thus we have to
+# disable this warning:
+#
+# SC2210 (warning): This is a file redirection. Was it supposed to be a comparison or fd operation?
+# https://www.shellcheck.net/wiki/SC2210
 # shellcheck disable=SC2210
 $x < 256
 $x < remarks

2019/burton/cow.sh

@@ -14,8 +14,8 @@ do if test -r "$name"; then
 	# (or, to use Bart Simpson's advice, make it 'not have a cow.sh'), as we
 	# actually need this to happen:
 	#
-	#   ^-- SC2086 (info): Double quote to prevent globbing and word splitting.
-	#
+	# SC2086 (info): Double quote to prevent globbing and word splitting.
+	# https://www.shellcheck.net/wiki/SC2086
 	# shellcheck disable=SC2086
 	set -- $s
 	((a += $1))

2019/burton/try.sh

@@ -15,15 +15,19 @@ make CC="$CC" all >/dev/null || exit 1
 # clear screen after compilation so that only the entry is shown
 clear
 
-echo "$ cat prog.c" 1>&2
+read -r -n 1 -p "Press any key to show prog.c: "
+echo 1>&2
 cat prog.c
 echo 1>&2
 
 for i in prog.c Makefile README.md; do
-    echo "$ ./prog < $i && wc < $i" 1>&2
+    read -r -n 1 -p "Press any key to run: ./prog < $i && wc < $i: "
+    echo 1>&2
     printf "prog: %s\n%4s: %s\n\n" "$(./prog < "$i"|tr -s ' ')" "wc" "$(wc "$i" | tr -s ' ')"
 done
 echo 1>&2
 
-echo "$ make test" 1>&2
+read -r -n 1 -p "Press any key to run: make test: "
+echo 1>&2
 make test
+echo 1>&2