ordering for custom value classes #142

Here is what the documentation indicates regarding ordered query:

ordered query

query {
  (entity: MyEntity) =>
    where(entity.attribute like "A*") select (entity) orderBy (entity.attribute)
}

If the entity attribute doesn’t support ordering, a compile error with be thrown.

There's no ordering support for a custom entity attribute.
That's to say if the attribute is neither a "String" nor an "Int", but a custom attribute, let's say a "Person" class for instance, the "desc" function won't work on such a class.