Proposal: Change key 'resource' to 'relation' in hasOne/hasMany object param.

[aars]

If it's still the case that the optional {resource: 'direct-reports', type: 'employees'} isn't documented (much/well) I want to suggest to rename the resource property of that object to relation. So:

Resource.extend({
  directReports: hasMany({relation: 'direct-reports', type: 'employees'}), // suggested
  // directReports: hasMany({resource: 'direct-reports', type: 'employees'}) // current
});

2 reasons:

1. Calling it resource is confusing since we're defining Resources all over the place, but that is not what it means in this case.
2. The related-proxy stores this value as relation. Which is what we end up using internally. meta.relation.

Many times there isn't really a resource (either defined in terms of ember-jsonapi-resources or defined in terms of a JSONAPI url/resource to request) by this name. It is the name of the relationship a Resource has with some other Resource of a certain type. As defined by type.
To illustrate using urls:
http://api.pixelhandler.com/api/v1/supervisors/1/relationships/`resource`
vs
http://api.pixelhandler.com/api/v1/supervisors/1/relationships/`relation`
would make more sense since:
http://api.pixelhandler.com/api/v1/direct-reports does not exist. It is not a resource.

(I'll be happy to do the work for this. Including changes to docs)

[pixelhandler]

@aars yes I agree the relationship link used to fetch the resource uses a relationship name. From the spec, "related resource" is what we're talking about operating on using a "relationship link" see http://jsonapi.org/format/#document-resource-object-relationships

I am in favor with using "relation" for the argument object property with the relationship helper.

I'm also curious if the helpers should be named toMany and toOne instead of hasMany and hasOne the nomenclature here:

• http://jsonapi.org/format/#crud-updating-to-many-relationships
• http://jsonapi.org/format/#crud-updating-to-one-relationships

We could keep the hasMany and hasOne as aliases as well. Here is a branch I started to explore the change https://github.com/pixelhandler/ember-jsonapi-resources/compare/attr-helpers-naming

[pixelhandler]

I'd like to add this as a 2.0 item