* Make assocations asserts easier to understand
* Refactor Association into Field like everything else
* Make assocation serializer/links/meta lazier
* Push association deeper into relationship
* Simplify association usage in relationships
* Better naming of reflection parent serializer
* Easier to read association method
* Move all associations related code from Serializer class to Associations module
* Introduce Reflection class hierarchy
* Introduce Association class
* Rid off Serializer#each_association
* Introduce Serializer#associations enumerator