Feature/round trip

First roundtrip spec. It reads a hale document, deserializes it, serializes it and compare the outcomes.
Note that this is a very minimal document. More specs are needed.
So, I don't think this is the interface we want to surface. I think the following is a better pattern:

```ruby
require 'representors/serialization/serialization_base'
require 'representors/serialization/serializer_factory'

module Representors
  class SerializerBase < SerializationBase
    def self.inherited(subclass)
      SerializerFactory.register_serializers(subclass)
    end

   # This method should return the serialized object as a hash or object or whatever is pertinent to the the media_type.
   def as_media_type(options = {})
      raise "Abstract method #as_media_type not implemented in #{class.name} serializer class.
   end
    
    ##
    # This method is overridden in child classes if a particular media-type format is required. Defaults to #as_media_type
    # unless overridden.
    #  @example
    #    # application/json
    #    def to_media_type(options = {})
    #       as_media_type(options).to_json
    #   end
    #
    def to_media_type(options = {})
      as_media_type(options)
    end
  end
end
```
What this will do is give us a public method on concrete implementations that the private #apply_serializations obscured so that you actually have a public method in the class itself. This was an issue @JordiPolo raised. 

In this case, HalSerializer class would implement:

```ruby
def as_media_type(options = {}))
  # apply_serialization(options) or whatever.
end

def to_media_type(options = {})
  as_media_type(options).to_json
end
```

And then the HaleSerializer class would just need to modify the #as_media_type method. 

@JordiPolo I have wanted to do some clean up refactoring around this stuff. Really did not get it all done to my satisfaction when I did some work here before. I am willing to merge this as is for now and refactor your stuff along these lines after you merge it to keep you going. Thoughts?