FitGames.Spine is an extension of the Spine Runtime, and the XNA supporting objects.
There is a new namespace added with two objects ContentAtlas and ContentSkeletonJson which inherit from SkeletonJson. These were created to load Spine objects from the content of the files instead of using a Stream or relying on XNATextureLoader.
The second, perhaps more important is because they are used in our MonoGame pipeline extension which allows zipping atlas.txt, skeleton.json, and skeleton.png into a zip file. This new zip file can be process by the pipeline and loaded using Content.Load<SpineAsset>('assetkey') with ease, and ready for rendering.