title: (discord.py) Client.send_message() doesn't send a message
body: <p>I'm using discord.py to create a chat-bot. As of now, it's only a test and all the code is in 1 file.</p>
  
  <p>The bot connects to the server and listens for messages starting with an Exclamation mark '!'.</p>
  
  <p>Depending on the command, it then calls one of 2 functions. Up to this point, the bot works as intended.</p>
  
  <pre><code>client = discord.Client()
  
  @client.async_event
  def on_message(message):
      author = message.author
      if message.content.startswith('!test'):
          print('on_message !test')
          test(author, message)
      if message.content.startswith('!quit'):
          print('on_message !quit')
          quit(author, message)
  </code></pre>
  
  <p>And this is where it gets weird. When the quit-function is called, the program terminates. When the test-function is called, it does nothing. It doesn't even print the string.</p>
  
  <pre><code>def test(author, message):
      print('in test function')
      yield from client.send_message(message.channel, 'Hi %s, i heard you.' % author)
  
  def quit(author, message):
      sys.exit()
  </code></pre>
  
  <p>What am i missing? Any help is appreciated.</p>