Save the model into a file.

    :param model: HTK model to be saved
    :param filename: File where to save the model

def save_model(model, filename):
    """Save the model into a file.

    :param model: HTK model to be saved
    :param filename: File where to save the model
    """
    with open(filename, 'w') as f:
        f.write(serialize_model(model))