created the initial Relation classes.
move HasMany under Relation.
coded HasJoin for join table relations.
add unlink methods in RelationInterface; returns $this from link and unlink methods.
add a Relation class as simple factory for various relationships.
maybe not to use static fetch method.
test Relation stuff. add tests class and models.
set $entity not in the constructor of Relation, but use entity method.
reflect the new id when saved to database.
add test for getting the related entity.
saves the relation object inside Entity object.
tested relation object are identical (same object are used as return).
tested link method in Has{One|Many} relation objects.
test against PostgreSql; renamed some traits and classes for clarification.
changed tag_id to varchar(64); used heredocs.
should reflect the original data to the just saved data, for both insert and update.
start testing HasJoin relation.
return key value of data if lastId is not used and ...
tested basic HasJoin relation object functionality.
test HasJoin for replacing (link method with array of entities).