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.
The error function now takes in a "RoutingError" structure. The idea is that the
structure includes all of the information necessary for a user to processor the
error as they wish. This interface is very incomplete and may change. At a
minimum, the error structure should include:
1) The request that failed.
2) Why the request failed.
3) The chain of attempted route matches, if any.
4) Something else?