Sleep Timer Suggestions (Patreon)

Sleep timer functionality is one of the most requested features on Github: https://github.com/generative-music/generative.fm/issues/19

Before I start working on it, I'd like to get some feedback about how this will be used.

- How long do you think you'll typically set this for?

- Do you need the ability to add time or otherwise change the timer after it's already been started?

- Should the music fade out before the time runs out? If so, about how long before the end of the timer should the music start fading out?

- Alternatively, does there need to be some audible indicator that the timer is up (like for Pomodoro, etc)?

- Any other comments or suggestions?

Thanks!