public void Save(GameState gameStateToSave)
{
XElement document = new XElement("root");
XElement gameStateElement = new XElement("GameState");
document.Add(gameStateElement);
gameStateToSave.Populate(gameStateElement);
string filePath = Path.Combine(Application.persistentDataPath, SAVE_FILE_NAME);
File.WriteAllText(filePath, document.ToString());
}