Hcore: Put everything in namespace hk::

hcore/include/simulator/simulator.h

@@ -4,6 +4,7 @@
 #include <config.h>
 #include <simulator/scene.h>
 
+namespace hk {
 namespace simulator {
 
 class Simulator {
@@ -19,6 +20,7 @@ private:
     Scene scene;
 };
 
-}
+} // namespace simulator
+} // namespace hk
 
 #endif // SIMULATOR_H