Initial work on introducing builder pattern for response

  * Added ResponseBuilderInterface & concrete implementation
  * Changed ResponseFactory into Director for managing response builder
  * Future notes:
  ** May want to extract large part of ResponseBuilder::buildResponse() into separate buildResponseModel().
  *** The only snag w/ this is that the Builder pattern doesn't seem to allow for passing in dependencies for building the different parts. This is where the Director would come in.
  ** May want to introduce additional director methods for creating each implementation of AbstractResponse
  ** The Builder pattern seems to work under the presumption that the director will handle specifying *how* the object is to be built (i.e. Part A, then Part C, then Part B). In which case, it may make the most sense to have a DirectorInterface, and several concrete implementations constructing objects based on API version, group, etc.
  *** This would move a large portion of the ResponseBuilder::buildResponse() body into separate implementations.
Injected default response types into Builder service def

  - Created exception layer to handle invalid configuration of ResponseBuilder
Add't cleanup work

  - Removed exception interface
  - Injected prototype model into builder
  - Removing ResponseDirector in favor of caller being Director
  - Updating README.md to reflect new usage approach
Merge pull request #1 from ReservedDeveloper/feature/responseBuilder

Feature/response builder
Updated documentation to use the standard _format

See http://symfony.com/doc/current/quick_tour/the_controller.html
Documentation fix

Removed unused parameter annotation
Removed unused INVALID_RESPONSE_FORMAT_CONFIG

It looks like the error string constant isn't being used. I agree with that decision; constants don't provide any added functionality to one-off error string generation.
Merge pull request #3 from mattjanssen/patch-1

Removed unused INVALID_RESPONSE_FORMAT_CONFIG