Abillity to Interrupt current fiber to give chance to other fibers

Usage example.

```
class WebsocketApiClient
  def connect
    # start websocket connection
    # setup incoming connection handler
  end

  def on_incoming_event(data)
    @events ||= []
    @events << data
  end

  def events
    EM::Synchrony.interrupt
    @events
  end
end

EM.synchrony do
  c = WebsocketApiClient.new
  c.connect
  puts c.events
  EM.stop
end
```