Integrate representors initial

@fosrias @sheavalentine-mdsol @miwest929 @HonoreDB 

DO NOT MERGE YET. 

This PR is not mergeable yet. (should be merged after #250 )
It includes initial RepresentorSerializer. Not everything is done correctly with regard to embedded items.

For embedded item, when called `embedded.to_representor(options)`, it then tries to call `to_media_type` on representor object, which is not what I would expect. I would expect to build representor object for entire target object and then call `to_media_type` on it. It means that I have to re-work media_type.rb a little bit.

```ruby
#representor_serializer.rb
      def get_embedded_data(options)
        object.each_embedded_semantic(options).map do |semantic|
          embedded_representor = semantic.value.map { |embedded| embedded.to_representor(options) }
          { semantic.name => embedded_representor }
        end
      end

#media_type.rb
          serializer = Crichton::Representor::RepresentorSerializer.new(self, options)
          representor = serializer.to_representor(options)
          representor.to_media_type(media_type, options)
```
@miwest929 @HonoreDB 
I believe this piece of code dispatches to the old serializers if they exist, and to Representor serializers if they don't.  Thus merging to Develop shouldn't break anything.

However this code is lacking sufficient test coverage.