Ideally there should be a way to request that the Stream gracefully exit. This might just be a `stop_tailing` method that sets a flag, and causes `run_forever` to exit if that flag is set.

Actually, if you're going to do that, it'd be awesome if you added the same interface to `Tailer`, so that you could call `@tailer.stop_tailing` and the next time through the mainloop it would exit immediately, instead of waiting for a batch of events to drain.