Flink's future abstraction whose API is similar to Java 8's CompletableFuture.
That's in order to ease a future transition to this class once we ditch Java 7.
The current set of operations comprises:

- isDone to check the completion of the future
- get/getNow to obtain the future's value
- cancel to cancel the future (best effort basis)
- thenApplyAsync to transform the future's value into another value
- thenAcceptAsync to register a callback for a successful completion of the future
- exceptionallyAsync to register a callback for an exception completion of the future
- thenComposeAsync to transform the future's value and flatten the returned future
- handleAsync to register a callback which is called either with the regular result
or the exceptional result

Additionally, Flink offers a CompletableFuture which can be completed with a regular
value or an exception:

- complete/completeExceptionally

…tion upon cancel