Implementing the sound system

With both sound emitter and sound listener components out of the way, we have a green light to begin implementing the sound system that is going to bring all of this code to life. Let's get it started!

class S_Sound : public S_Base{
public:
  S_Sound(SystemManager* l_systemMgr);
  ~S_Sound();

  void Update(float l_dT);
  void HandleEvent(const EntityId& l_entity,
    const EntityEvent& l_event);
  void Notify(const Message& l_message);

  void SetUp(AudioManager* l_audioManager,
    SoundManager* l_soundManager);
private:
  sf::Vector3f MakeSoundPosition(const sf::Vector2f& l_entityPos,
    unsigned int l_elevation);
  void EmitSound(const EntityId& l_entity,
    const EntitySound& l_sound, bool l_useId, bool l_relative,
    int l_checkFrame = -1);
  AudioManager* m_audioManager;
  SoundManager* m_soundManager;
};

Apart from the typical methods that a system is required to implement and a few custom ones, we also have two data members...