Return an instance of Response from responders, hooks, middleware

[kgriffs]

Let's explore the ramifications of having responders, hooks, and middleware methods return an instance of Response rather than simply editing resp in-place. Note that Hooks and middleware may choose to simply pass along an instance of resp that they receive.

[vytas7]

Even if we decide in favour of this, we cannot afford such a big restructuring in 4.0 due to time constraints, rescheduling.