Add try scripts to 1993/plummer

The two scripts allow one to specify the number and the arg
(corresponding to the argv[1] and argv[2] of the program). The alt
script has a way to redefine the SLEEP variable (in the Makefile) like

    SLEEP=500 ./try.alt.sh

1993/plummer/try.alt.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+#
+# try.alt.sh - demonstrate IOCCC winner 1993/plummer alt code
+#
+
+# make sure CC is set so that when we do make CC="$CC" it isn't empty. Doing it
+# this way allows us to have the user specify a different compiler in an easy
+# way.
+if [[ -z "$CC" ]]; then
+    CC="cc"
+fi
+
+# let user change the sleep duration if they wish
+#
+if [[ -z "$SLEEP" ]]; then
+    SLEEP=1000
+fi
+
+# let user change the number if they wish to
+#
+if [[ "$#" -lt 1 || -z "$1" ]]; then
+    NUMBER="01234567890876543210"
+else
+    NUMBER="$1"
+fi
+
+# let user change the arg if they wish to
+#
+if [[ "$#" -lt 2 || -z "$2" ]]; then
+    ARG="xxx"
+else
+    ARG="$2"
+fi
+
+make clobber CC="$CC" SLEEP="$SLEEP" alt >/dev/null || exit 1
+
+# clear screen after compilation so that only the entry is shown
+clear
+
+echo "$ ./plummer.alt $NUMBER $ARG" 1>&2
+read -r -n 1 -p "Press any key to continue (send intr/ctrl-c to terminate): "
+echo 1>&2
+./plummer.alt "$NUMBER" "$ARG"