Allow the use of Go templating engine in rewrite middleware.
Rewrite middleware treats response body as a template.
Added flag for optional body rewriting for rewrite middleware.
More efficient template processing for the rewrite middleware.
Simplify body closing logic for the rewrite middleware.
Added redirect flag to the rewrite middleware.
Fix code review comments.
Merge pull request #123 from mailgun/roman/rewrite

Enhance rewrite middleware.