(refactor) Removed Alloy and use AnyMap directly.
(feat) Implement Extensible for Request and Response. [Fixes #133]
Merge pull request #136 from reem/feat/plugin

Implement Plugin System
(refactor) Make body optional to mark when body was written to.
(hotfix) Expose Extensible.
Merge pull request #139 from reem/feat/opt-body

(refactor) Make body optional to mark when body was written to.
(feat) Implement Show for Url.