Add Future::flatten #404
Description
Similar to future-rs's Future::flatten method, this can sometimes come in useful.
However the only difference with it should be that we take IntoFuture as the trait bound, and call it under the hood. Because IntoFuture is implemented for Future this should work as expected.
Thanks!
Examples
let nested_future = async { async { 1 } };
let future = nested_future.flatten();
assert_eq!(future.await, 1);