Avoid busy loop

[benjie]

Add a short sleep command to the main while True: for when there are no events; maybe 0.1s?

[Yommy]

ah, that time.sleep(3) got too indented

[Yommy]

could be reduced time also

[benjie]

The sleep(3) where you have it makes sense because it prevents the bot accidentally flooding Slack; however a reasonable delay when just waiting for events in the idle state makes sense too. Since events are pooled together it's okay to wait a bit longer (e.g. 0.1s doesn't limit us to receiving 10 events per second and thus trigger a huge queue), but we want to seem responsive.