trying out d3

Yup. I think `r` should maybe just be some static value in the `circle` drawing. I guess we could do one of two things:
  - Create a new `state` component and ditch circle after this PR (which would mean we wouldn't have to worry about adding `x` and `y` to the data for now).
  - Rename `circle` to `state` and change it to do the drawing `state` will be doing.

Either way, we'd ended up with the same thing, so your call.