Fiber API questions

[Fabio Tudone]

Hi, I have some questions about the current "Fiber" API:

- Why the constructors accepts only a "Runnable" and not a "Callable"?
- Why on the other hand the static "Fiber#schedule" method doesn't return a
"Fiber" but rather a "CompletableFuture"?

This allows "Fiber" to avoid being generic (is there a specific reason for
that BTW?) but it forces the user to choose between getting back a "Fiber"
reference and being able to throw checked exceptions in the fiber code.

Thanks,
-- Fabio