Only one change this time around: Splitting Serializer methods for item and collection to be their own thing.
This was done to fix #71 as well as make life easier for people who want to make items and collections use some different logic. For example, JsonApiSerializer wants even a single item to appear inside an array, meaning we can wrap the data in the item() serializer method to do that, but keep it as an item in case anyone wants to switch to a different serializer.
See Serializers documentation for more information.