Countable relations, id encoding and non-Eloquent resources

Added

• #18 Added a withCount query parameter. For Eloquent resources, this allows a client to request the relationship count for the primary data's relationships. Refer to documentation for implementation details.
• #55 Encoding and decoding of resource IDs is now supported. The ID field needs to implement the LaravelJsonApi\Contracts\Schema\IdEncoder interface for this to work.
• #41 Hash IDs are now supported by installing the laravel-json-api/hashids package and using the HashId field instead of the standard Eloquent ID field. Refer to documentation for details.
• #30 Non-Eloquent resources are now supported via the laravel-json-api/non-eloquent package. Refer to documentation for implementation details.
• There is now a Core\Reponses\RelatedResponse class for returning the result for a related resources endpoint. For example, the /api/v1/posts/1/comments endpoint. Previously the DataResponse class was used. While this class can still be used, the new RelatedResponse class merges relationship meta into the top-level meta member of the response document. For to-many relationships that are countable, this will mean the top-level meta member will contain the count of the relationship.
• The schema generator Artisan command now has a --non-eloquent option to generate a schema for a non-Eloquent resource.

Changed

• The LaravelJsonApi::registerQuery(), LaravelJsonApi::registerCollectionQuery() and LaravelJsonApi::registerRequest() methods must now be used to register custom HTTP request classes for specified resource types. Previously methods could be called on the RequestResolver classes, but these have now been removed.

Fixed

• Relationship endpoints that return resource identifiers now correctly include page meta in the top-level meta member of the document, if the results are paginated. Previously the page meta was incorrectly omitted.