Modularize the source code.

This makes greeting generation separate from greeting output, which
makes it easier to unit-test greeting generation.

Change-Id: Ice07f45ed0e9274bd4d4b3cd031cb37fffd34a5e
diff --git a/exe/hello-world-ng.cpp b/exe/hello-world-ng.cpp
new file mode 100644
index 0000000..f59229c
--- /dev/null
+++ b/exe/hello-world-ng.cpp
@@ -0,0 +1,9 @@
+#include <mod/greeting.hpp>
+
+#include <iostream>
+#include <cstdlib>
+
+int main(int, char **) {
+  std::cout << greeting::make_greeting("world") << std::endl;
+  return EXIT_SUCCESS;
+}