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.
Callers may not always have `futures` available at the root of the
crate. Re-exporting dependencies makes them available to the macro at a
deterministic location.
Carl Lerche