improve optionals and futures.
improve optionals and futures.

Summary:
Add and assign to options bindings.
Add a isReady to future bindings

Reviewed By: yfeldblum

Differential Revision: D13667465

fbshipit-source-id: 8522ef59d7d262cc13dc9f9940c37b7a0b65870c

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly