message: Use caf_main in hello_world example
diff: @@ -33,13 +33,13 @@ void hello_world(event_based_actor* self, const actor& buddy) {
  );
  }
  -int main() {
  - // our CAF environment
  - actor_system_config cfg;
  - actor_system system{cfg};
  +void caf_main(actor_system& system) {
  // create a new actor that calls 'mirror()'
  auto mirror_actor = system.spawn(mirror);
  // create another actor that calls 'hello_world(mirror_actor)';
  system.spawn(hello_world, mirror_actor);
  // system will wait until both actors are destroyed before leaving main
  }
  +
  +// creates a main function for us that calls our caf_main
  +CAF_MAIN()
  