Sound

We could support programmatic generation of sound by using a function Number -> Number (time to amplitude sample). The sampling frequency would need to be FAR higher than the animation frequency, so we'd batch it and use a buffer.

Problems:
- The [JavaScript audio API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API) doesn't work with Internet Explorer (possibly other browsers).
- Performance would be a challenge, and we need to make sure this can be done efficiently to avoid stuttering, even on slow computers.
- It's not clear how to merge this into games. The obvious way would be

audibleInteractionOf(initial, step, event, draw, sound)

But this ties the audio sample rate to the frame rate, which is bad. Another way would be to maintain a different World type for sound, but this is too complicated. Definitely could use some thought.
- We'd need a reasonable kind of abstraction that doesn't involve new ADTs with complicated behaviors. Working directly with wave forms might be an educational experience for a bit, but it shouldn't be unreasonably hard to just choose a timbre and play a melody.