Implemented Promises support

[ydaniv]

Notice on stop I reject the promise with the chained context. I know it's contrary to what Dominic said but it seemed to be the best solution, and I couldn't find anything in the specs about the reason having to be an error.

Also, I went over the code and think I covered all places where you return from the animate method, so please check if I missed anything.

[ydaniv]

Continue from #87.

[mikaelkaron]

It is possible that @domenic will poke you with something sharp for rejecting without there actually being an error. From what I can understand that's a no-no.

I think that rejecting with a a reason that is not instanceof Error is OK (it makes life a lot easier in promise libs like when.js that can replicate try/catch logic in an async fashion, but hardly a requirement)

[ydaniv]

@mikaelkaron that's cool. My intention was to get this out there so that we can decide on the optimal solution.

How would you expect a promise to behave for a stopped animation? Fulfill it? Reject it?

[domenic]

Is stopping an animation an exceptional situation? I.e. if this was a synchronous function, would it thrown an exception?

[ydaniv]

@domenic thanks for the link! this is quite helpful. Since this is an act initiated by the user I guess it won't count as an exceptional situation.

In a sync promises-less API the user expects the usual flow, however, the complete callback should not be invoked, and it does when resolving a promise.

So I guess we should resolve it, but still somehow suppress the complete callback.
Let me give it a try.

[ydaniv]

Oh! Silly me 👻 resolving will just resolve and not do anything else.

[julianshapiro]

This is about 1 day away from being implemented.

[julianshapiro]

Integrated. See http://velocityjs.org/#promises. Thank you for your help, @domenic and @mikaelkaron.