
Pubsub notifications
---------------------

It can be useful, at least during application development, to 
have some code called when pubsub takes certain types of actions. 
Pubsub supports "notification handlers" and notification flags: 

* a *notification handler* is an instance of a class that defines 
  several methods to handle one, more or all of the types of 
  notifications supported by pubsub
* a *notification flag* is a boolean used to toggle a particular
  type of notification on or off; there are several types of 
  notifications::
  
	subscribe
	sendMessage
	newTopic
	delTopic
	listenerDead
	
The notification flags are changed via pub.setNotifications():
  
A notification handler must adhere to the INotificationHandler
protocol defined in pubsub.utils modules::

	import pubsub.utils
	class MyNotifHandler(INotificationHandler):
		def onSendMessage(...):
	
	pub.addNotificationHandler( MyNotifHandler() )
	
A notification handler is held by strong reference.


