v4.0

This breaking release removes the isPlaying boolean; tracking that state was causing additional re-renders, which could pile up when using multiple instances of the hook.

If you were relying on this prop, you can implement it yourself using the onplay and onend events from Howler. An example is shown here: https://github.com/joshwcomeau/use-sound/blob/master/stories/demos/ShowWhilePlaying.js