Serialize ids as strings in JSON-API adapter
Merge pull request #685 from ride/ids-as-strings-2

Serialize ids as strings in JSON-API adapter
Fix support for custom root in JSON-API adapter
Renamed embed test to have "test" suffix
Fixed reference to association options
Merge pull request #689 from ride/fix-json-api-custom-root

Fix support for custom root in JSON-API adapter
Merge pull request #691 from jacob-s-son/fix-embed-option-for-associations

Fix embed option for associations
Handle correctly null associations

null belongs_to associations are now serialized as nil instead
of raise an error during serialization.
Merge pull request #708 from ride/fix-for-nil-associations

Handle correctly null associations