Added before and after callback support to the middleware. Filter out bad headers from prerender service request that will leave requests hanging.
Better naming for phantomjs filtered headers constant.
remove debug logging
made build_rack_response_from_prerender configurable so that DISALLOWED_PHANTOMJS_HEADERS can go there
added a test and incremented version
added documentation for build_rack_response_from_prerender
Merge pull request #5 from collectiveip/callback-support

Caching callback support