yaranullin/event_system.py: major changes
yaranullin/event_system.py: major changes

 1. turn _EVENTS into a defaultdict(set);

 2. change '__event__' to 'event' and '__id__' to 'id';

 3. connect()
   * abort if event is not an integer;
   * abort if already connected;
   * save callbacks using WeakCallback;

 4. disconnect()
   * do not check anymore for the key 'ANY' in _EVENTS because _EVENTS is now
     a defaultdict;
   * provide a _disconnect() function to disconnect just one element;

 5. post()
   * accept also a dictionary as argument;

 6. process_queue()
   * do not inspect anymore the arguments of every handler;
   * support handlers with no arguments;
   * take care or garbage collect dead WeakCallback inside _EVENTS;

ciappi/Yaranullin