Added a simple PubSub library

This library injects a simple PubSub framework into any object. 

Sample Use:
// Inject PubSub into your object
var myObject = {};
PubSub(myObject);

// Add an event and define your callback
myObject.on('someevent', function(args) {
   // Do something
});

// Add an event and get the token representing this callback
myObject.on('someotherevent', 'my token', function(args) {
   // Do something
});

// Trigger the event
myObject.trigger('someevent', { somekey: 'somevalue' });


// Remove a specific event by it's token
myObject.off('my token string');