Make SSEView an iterator.
Make SSEView an iterator.

* Use __iter__() and next() so that I can raise
  StopIteration when needed.
* Previously, when clients disconnected, the infinite loop
  in iterator() caused a memory leak, so it's better to use
  next() so I can return a message at a time.
* Track running time, so I can raise StopIteration
  when timeout is reached.

toffer/minecloud,toffer/minecloud