- start_new is a classmethod that creates Timeout and starts it
- start() will now raise AssertionError if called when already started()
- although it's OK to do "with t" even if t is already started
- when start_new is passed a Timeout instance it simply returns it;
  this allows to customize timeout exception in many places by passing Timeout
  instance instead of number of seconds

--HG--
rename : examples/wsgi.py => examples/wsgiserver.py

- to check gevent.Event API conformance

- this makes Event API compatible with threading.Event
- compatibility with Queue.put is not need, because Greenlet does not threat put/put_exception
  as special method names the way Proc did it
- put and put_exception still available but raise deprecation warnings

- start event is stored as an attribute; it is cancelled by throw()
- spawn_later returns Greenlet instace, not tuple (greenlet, event)
- _run / args / kwargs attributes are removed when Greenlet finishes execution