Improve alt build of 1989/ovdluhe

One can now do

    make clobber P=5 alt

instead of the more awkward

    make clobber CDEFINE="-DP=5" alt

The try.alt.sh script was added and allows one to do

    P=5 ./try.alt.sh

If P is not specified it uses the default of the alt code (which checks
if it's defined first via #ifdef..#endif). Otherwise it uses the new
value. Of course if one specifies not an int or too high value (or maybe
too low - didn't try that) the program will fail. That is the fault of
the user. The author does note a reasonable range to try.

1989/ovdluhe/try.alt.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+#
+# try.alt.sh - demonstrate IOCCC winner 1989/ovdluhe.alt 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
+
+# user may also reconfigure P
+if [[ -n "$P" ]]; then
+    make clobber CC="$CC" P="$P" alt >/dev/null || exit 1
+else
+    make clobber CC="$CC" alt >/dev/null || exit 1
+fi
+
+# clear screen after compilation so that only the entry is shown
+
+i=0
+for ((i=0; i<4; ++i)); do
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < ovdluhe.alt.c: "
+    echo 1>&2
+    ./ovdluhe.alt < ovdluhe.alt.c
+    echo 1>&2
+
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < README.md: "
+    echo 1>&2
+    ./ovdluhe.alt < README.md
+    echo 1>&2
+
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < Makefile: "
+    echo 1>&2
+    ./ovdluhe.alt < Makefile
+    echo 1>&2
+done