Record binder with custom id field.

In the RDF world Resource URI is matter, but currently RecordBinder do not take this into account.

In my use case I need to have PointedGraph pointer to be available as case class field. And also sometimes I want create new resource with some URI and serialize it to PointedGraph. 

This pull request should be considered only as example of what I am trying to do. I've implemented it in a very dirty manner and it would be great if someone can help me to make it in a more idiomatic way. Any ideas are welcome and thanks in advance.