Update Tokio to use std::future. (#1120)

A first pass at updating Tokio to use `std::future`.

Implementations of `Future` from the futures crate are updated to implement
`Future` from std. Implementations of `Stream` are moved to a feature flag.

This commits disables a number of crates that have not yet been updated.

tokio-sync/src/task/mod.rs

@@ -1,5 +1,5 @@
 //! Thread-safe task notification primitives.
 
-mod atomic_task;
+mod atomic_waker;
 
-pub use self::atomic_task::AtomicTask;
+pub use self::atomic_waker::AtomicWaker;