title: Telegram bot (pyTelegramBotAPI) does not handle new user joining group
body: <p>I have recently created a simple bot for telegram using the pyTelegramBotAPI (telebot).
  I added a message handler that is supposed to handle <strong>every</strong> message, including the ones that appear on a group when a new user joins, which are still <code>Message</code> objects a non-null <code>new_chat_members</code> property.</p>
  
  <pre class="lang-py prettyprint-override"><code>import telebot
  bot = telebot.TeleBot(TOKEN)
  
  [...]
  
  @bot.message_handler(func=lambda m: True)
  def foo(message):
      bot.send_message(message.chat.id,"I got the message")
  
  
  
  bot.polling()
  
  </code></pre>
  
  <p>Even so, the bot does not reply with the "I got the message" string when I add a new user, although it does catch other messages.</p>
  
  <p>Why is this happening? Is this a problem about the message handler? Is there maybe a more general handler that is sure to catch every update?</p>
  
  <p>Thank you</p>