revert to active support concern for sake of dependency management
fix capitalization error
fix callbacks for inherited controllers, append to controller registry using implements method
Refactored controller concerns
* Split Controller into Controller and Callback concerns
* Added a sharing and inheritance case example:
** Added more a controller/definition/mediatype for Volumes resource
** Made Instances and resources to include a common “BasicApi” concern (which will make them share filter concerns)
** Made Instances and resource to inherit from a base class (and added some warning text about not to use object inheritance for sharing concerns)
** Changed the common trait to define an optional Auth header
**  build a functional tests using it.
** Introduced a ‘concerns’ directory in the spec_app 
* Enable direct attribute setting inside the headers DSL. Careful with the case sensitivity as Rack treats all headers as uppercase.
* Moved request/response in Controller trait back to attr_reader/accessor

Signed-off-by: Josep M. Blanquer <blanquer@rightscale.com>
Added specs for around callbacks and refactored controller specs
Filled in the Changelog

Signed-off-by: Josep M. Blanquer <blanquer@rightscale.com>
Merge pull request #32 from blanquer/concerns_and_inheritance

Concerns and inheritance