For REVIEW: Initial attempt at a json_home serializer

- didn't know how to automatically register a serializer, so a JsonHomeSerializer is newed in EntryPoints.to_media_type
- Added in entry_points.yml in spec/fixtures/entry_points
-Html serialization will be another effort altogether. Can A) Generate it manually. B) Convert EntryPoints object array into a form usable by the default html serializer to generate links.