Implicitly return slice/array

[cmin764]

Is there any obvious reason for which the intersection returns an interface{} instead of []interface{}? I think each time we do an intersection we expect to end up with an array/slice and not manually make that conversion each time.
Maybe I'm missing some casting edge-cases where this generic response makes sense.

[juliangruber]

Good point, I don't think it needs to be interface{}. Do you want to try this in a PR?

[cmin764]

Yes, how about this: #5 ?