This is a breaking change.
The `testing` feature no longer exists. Testing structures can now be
accessed without any features enabled.
Prior to this change, Rocket would panic when draining from a network
stream failed. With this change, Rocket force closes the stream on any
error.
This change also ensures that the `Fairings` launch output only prints
if at least one fairing has been attached.
This is a breaking change. A call to `Response::headers()` can be
replaced with `Response::headers().iter()`. A call to
`Response::header_values()` can be replaced with
`Response::headers().get()`.