Also:
* Remove 'response::ResultFuture'.
* Re-export 'tokio' and 'futures' from the crate root.
* Make 'ResponseBuilder::sized_body()' and 'async fn'.
* Remove the 'Future' implementation for 'ResponseBuilder'.
* Add 'ResponseBuilder::finalize()' for finalizing the builder.
In order to avoid making 'ResponseBuilder::sized_body' an asynchronous
function, the seeking is deferred until finalization. 'finalize()' is
replaced with '.await', and 'ResponseBuilder::ok()' is an 'async fn'.
* body_string_wait and body_bytes_wait are removed; use `.await` instead
* `dispatch()` is now an async fn and must be .await-ed
* Add `#[rocket::async_test]` macro, similar in purpose to `tokio::test`
* Tests now use either `rocket::async_test(async { })` or
`#[rocket::async_test]` in order to `.await` the futures returned
from `dispatch()` and `body_{string,bytes}()`
* Update 'test.sh' to reflect the tests that should be passing.
Broken:
* Cloned dispatch and mut_dispatch() with a live previous response now both fail, due to a (partial) check for mutable aliasing in LocalRequest.
* Some tests are still failing and need example-specific changes.
Sergio Benitez
Michael Howell
Jeb Rosen
Jacob Pratt