Naming: FutureLike, Future, Complition

[EdmondDantes]

The following names are proposed to resolve the naming conflict for Future:

1. Current: FutureLike, Future extends FutureLike
2. Completable interface, Future extends Completion
3. Future interface, Completion implementation

[bwoebi]

Completable and Future are both fine by me. Just not FutureLike please :-D