Completes.recoverFrom() should support a handler that returns a Completes<Y> not just Y

[bwehrle]

Scenario:

• Complete needs to be turned into a Completes
• If there is an error, invoke a .recoverFrom()

Imagine that the function inside the recovery handler returns a Completes

From inside the recoverFrom(), I would not want to do a await() on the inner Completes, I'd rather return the Completes directly, since that is what the outer code block is expecting as a result. Otherwise I need to do some kind of await() call just to return a Y which will just be turned into a Completes with the outcome already provided, making the thread block.