Improve cljs callback experience

[peterschwarz]

Either:

• use a more Node-stye callback signature. For example:

  (open-serial-board :auto-detect (fn [err board]
     ; Do stuff with the board
     )
  

• Return a Promise or promise-like structure for the board result.

[metasoarous]

Nice call. I'd be inclined to say callbacks, since they're ultimately simpler, and you can still hook a promise up to it. Then again, perhaps you could have two arities; one that takes a callback, and one that just returns a promise? That would give some added flexibility.

FWIW, I'm leaning towards callbacks for pin-ctrl...