Support proper error objects

[jfhs]

Specification proposes layout of errors part of the output. Currently available fields in Internal\Error are: title, detail and status. Specification has more fields, and library should allow user to set them.

Another issue is that it is currently formatter expects only single Error in response, it should also support ErrorCollection. Maybe a special exception JsonApiMultipleErrors, or something like that can be added, so that user can return multiple errors conveniently.

Ideally, there might be some support of validation (I don't know which one, does .Net core/EF has one?) and automatic exceptions if some fields are invalid thrown from Controller/DefaultRepository, with correct pointers to fields.

[jaredcnance]

A couple things I think we can do:

• Make JsonApiExceptionFactory a service so that it can be replaced by the users.
• I think a special multi-exception is a good suggestion (or maybe just an overload for the current JsonApiException), its constructor might look like this.

 public JsonApiMultiException(ErrorCollection errors);

Users could customize the error object by inheriting from Internal.Error and adding properties as necessary. Then to throw the exception:

var myCustomErrors = new MyCustomErrors();
throw new JsonApiException(myCustomErrors);

What do you think?

[jaredcnance]

This is now available in the v1.2.0 pre-release. See the updated documentation for usage.