Modifications to event API:
  - Event base class requires source and name arguments
  - Removed EventEmitter.__init__ connect argument
  - Removed EmitterGroup__init__ event_names argument
  - EmitterGroup.add accepts multiple event specs as keyword arguments
  - Added stub Event subclasses
Merge branch 'master' of github.com:vispy/vispy

Conflicts:
	vispy/event.py