Add support for outbound rules in rewrite middleware

As an extension on my implementation of UrlRewrite, Outbound rules will look through an Http response for any regex match, and replace them appropriately.
Documentation here:
http://www.iis.net/learn/extensions/url-rewrite-module/creating-outbound-rules-for-url-rewrite-module
http://www.iis.net/learn/extensions/url-rewrite-module/url-rewrite-module-20-configuration-reference

The big problem here will be perf, as we are going to regex match on the whole body of the response.

This would probably be an extension on top of the rewriter.