One-to-One Mapping Support

Please add a more convenient OneToOne mapping attribute inspired on the Java's Hibernate @OneToOne:

Hibernate ORM 5.5.9.Final User Guide.

This feature is too important to not have the need to use ManyValuedAssociation thus avoids the use of wrapper does not need to instantiate a TList avoiding overload, making it more natural, because it doesn't make sense to create a list to retrieve only a single object

Suggestion create OneToOneAssociation option we will be happier with this option, Thanks.