Adds a `$reference` method to the `$kinvey.User` definition

The `$reference` method can be used to return a reference to the entity represented by the resource instance: http://devcenter.kinvey.com/rest/guides/datastore#setup.

Reference: issue #19.
Adds a `$reference` method to the `$kinvey.Object` definition

The `$reference` method can be used to return a reference to the entity represented by the resource instance: http://devcenter.kinvey.com/rest/guides/datastore#setup.

Reference: issue #19.
Adds a `$reference` method to the `$kinvey.File` definition

The `$reference` method can be used to return a reference to the entity represented by the resource instance: http://devcenter.kinvey.com/rest/guides/datastore#setup.

Reference: issue #19.
`$kinvey.Object.$save` demonstrates deep reference recognition

When saving an object the `$reference` method is used as a marker to detect and flatten nested Resource instances into references.

Reference: issue #19.
`$kinvey.File.$save` demonstrates deep reference recognition

When saving an object the `$reference` method is used as a marker to detect and flatten nested Resource instances into references.

Reference: issue #19.
`$kinvey.User` demonstrates deep reference recognition in saving methods

When saving an object the `$reference` method is used as a marker to detect and flatten nested Resource instances into references. Methods which display this functionality are `$login`, `$signup` and `$save`.

Reference: issue #19.
Merge pull request #23 from ninjatronic/v2-dev-object-detection

Automatically detects deep-nested $kinvey objects and replace with references