New API methods:
GET /v1/stories/:story_id/story_fragments	Returns available fragments of a story.
GET /v1/stories/:story_id/story_fragments/:id	Returns a fragment of a story.
POST /v1/stories/:story_id/story_fragments	Create a fragment of a story.
PUT /v1/stories/:story_id/story_fragments/:id	Update a fragment of a story.