YUI Custom Events
    Custom event system

3.0.0
    - Broken into core base and complex modules.
    - broadcast works for simple events.
    - If configured to return an event handle, the return value
      will always be a single object, regardless of how many listeners
      were attached.  Previously, multiple listeners provided an array
      of detach handles.

3.0.0beta1
    - Implemented the broadcast flag.  broadcast = 1: local, accessible
      via Y.on('prefix:event'). broadcast = 2: global, accessible
      via Y.on or globally via Y.Global.on('prefix:event).  Broadcast 
      listeners cannot effect the defaultFn or host subscribers (so
      are in effect, after listeners), although this is still possible
      by added either Y or Y.Global as event targets.
    - Moved custom event out of event package
    - EventTarget accepts a prefix configuration.  This is used
      in all exposed methods to handle shortcuts to event names,
      e.g., 'click' and 'menu:click' are the same if the prefix
      is 'menu'
    - Exposed methods are 'on' for the before moment, 'after' for
      the after moment, and 'detach' for unsubscribe.  subscribe,
      before, unsubscribe, and corresponding methods are deprecated.
    - Event type accepts a event category which can be used to
      detach events.  
      Y.on('category|prefix:event', fn);
      Y.detach('category|prefix:event');
      Y.detach('category|*');
    - Added 'chain' config to events that makes the return value the 
      event target rather than a detach handle.  Use with the detach
      category prefix.
    - The type parameter can be an object containing multiple events to attach
      Y.on( { 'event1': fn1, 'event2': fn2 }
    - Y.fire payload for event facades can be another facade or a custom event.