Preprocess string to transform all diacritics and remove other special characters than appropriate
    
    :param string:
    :return:

def preprocess(string):
    """
    Preprocess string to transform all diacritics and remove other special characters than appropriate
    
    :param string:
    :return:
    """
    string = unicode(string, encoding="utf-8")
    return regex.sub('', string).encode('utf-8')