🚚 Moved 'Hello World' into its own project subfolder.

src/hello/hello_world.cpp

@@ -0,0 +1,6 @@
+#include <iostream>
+
+int main() {
+    std::cout << "Hello World!" << std::endl;
+    return 0;
+}

src/hello_world.cpp

@@ -1,8 +0,0 @@
-#include <iostream>
-
-using namespace std;
-
-int main(int argc, char *argv[]) {
-    cout << "Hello World!" << endl;
-    return 0;
-}