- Fixed subscription limits
   {
     'max_total_subscriptions': None,
     'max_total_connections': None,
     'max_subscriptions_per_connection': None,
     'subscription_push_rate_limit': None, # in seconds
   }
   (some were previously located under {'connection_defaults': })
 - {'connection_defaults': {'unpack_json': ...}} option
    False = messages are forwarded to .handle as is
    True = messages are attempted to json load first
    'force' = -||- but logs and skips the unloadable objects
 - {'vebose': ...} option
    1 = connection, subscription, send events
    2 = 1 + ping events + some inner mechanisms
    3 = 1 + 2 + recv events
 - detect if message is a ping, and response with a pong
   {
     'connection_defaults': {
       'pong': pong_function,
       'pong_as_message': True,
     }
   }
   pong_function
    accepts received message as first arg
    returns:
     a) `None` if message is not ping
     b) the pong message to be sent back
   pong_as_message
    False = send pong msg via socket.pong
    True = send pong msg via socket.send (default)
    'dump'= -||- but msg is json encoded first
   ping_as_message
    -||- but False by default