PlayPrefsManager

	const string MASTER_VOLUME_KEY = "master_volume"; 
	const string DIFFICULTY_KEY = "difficulty"; 
	const string LEVEL_KEY = "level_unlocked_"; 
	const string SURVIVAL_MODE_KEY = "survival_mode";

	public static void SetMasterVolume (float volume){
		if (volume >= 0f && volume <= 1f) {
			PlayerPrefs.SetFloat (MASTER_VOLUME_KEY, volume);
		} else {
			Debug.LogError ("Master volume is out of range! Noooo!");
		}
	}

	public static float GetMasterVolume() {
		return PlayerPrefs.GetFloat (MASTER_VOLUME_KEY);
	}

	public static void SetSurvivalMode(float survival){
		if (survival >= 0f && survival <= 1f) {
			PlayerPrefs.SetFloat (SURVIVAL_MODE_KEY, survival);
		} else {
			Debug.LogError ("Survival mode is out of range!");
		}
	}

	public static float GetSurvivalMode (){
		return PlayerPrefs.GetFloat (SURVIVAL_MODE_KEY);
	}