Remove punctuation marks, articles
    and bot appeals (like 'hey bot')

    :param message_text: user's message text
    :return: normalized message text

def normalize_message(message_text):
    """
    Remove punctuation marks, articles
    and bot appeals (like 'hey bot')

    :param message_text: user's message text
    :return: normalized message text
    """
    for mark in PUNCTUATION_MARKS:
        message_text = message_text.replace(mark, ' ')
    # Add barier elements for not deleting middle of word
    message_text = ' ' + message_text + ' '
    for article in ARTICLES:
        message_text = message_text.replace(article, ' ')
    # Delete extra spaces
    message_text = ' '.join(message_text.split())
    # TODO: Delete bot appeals (like 'hey bot', 'hi', 'bot') if it's not
    #       the only content of message
    return message_text