Implement `peek` on `event/emittable`.

Implement `spy` on `pubsub/hub` and `component/gadget`.
Emitter tests should be async.
Added test for reject
Added test for reject
Bump version to 3.0.0-1
Merge pull request #125 from troopjs/feature/peek-and-spy

Add method on emittable to get latest emitted value
Dep versions -> `develop`
Merge branch 'develop' into feature/docs