(feat) Added Redirect, a modifier for setting the location header.
(chore) Deprecate many existing Response constructors in favor of modifiers.
(chore) Expose Set.
(refactor) Stream response bodies to clients instead of re-allocating.

The new .set(Body) feature sets content-length appropriately and is
far more amenable to streaming than the previous scheme, this allows
us to get away with a more performant scheme.