Added Element.HasAttribute
Blocked attributes called "name" or "id"
Fixed setting Datamodel.Root to null
More docs and exception message improvements
Fixed importing Elements with empty Element attributes
Optimised Element import a bit
Fixed Element import crushing Vector4 to Vector2
Custom exceptions now derive from more specific classes
Added ElementOwnershipException
Readme tweaks
Added Element Import test
All tests now include one recursive element and one stub element