Cleaner examples

- Use ${CXX} instead of explicit clang in the Makefile.
- More explanations.
- Use socat's fork option instead of a bash loop.
- Adds a run_* script for each example.
- Remove the useless "sleep" option in service2.

run_pcat.sh

@@ -0,0 +1,8 @@
+
+# Start the service and let it run in the background.
+./pcat data &
+PID_SERVICE=$!
+
+echo "Hello world!" > data &
+
+KILL $PID_SERVICE