Make Sync extend Defer

[johnynek]

now that Defer has landed in cats 1.2.0, I think Sync should extend Defer[A] with def defer[A](fa: => F[A]): F[A] = suspend(fa).

Defer is not about side effects, but suspend can also handle those, so it seems only more general, since if side effects are allowed to happen, it can't have evaluated before returning.

[alexandru]

👍 can you do a PR?

[alexandru]

Would be cool if this made it in 1.0.0-RC3.

Who's up for a PR?

[Avasil]

I guess I can take a look at it today @alexandru

[alexandru]

👍 @Avasil go for it