F/default serializers

Adds Default Serializer Classes
As well as an afterSerialize Callback
A set of optional and required fields to be serialized
Might there be cases where the post-processor needs data from the original (Cake) array in order to operate properly? The already-processed (json-api) array might not contain enough information anymore. I was expecting the signature to be `function afterSerialize($original, $processed)` essentially.