Fix primitive serializations by returning actual object

[koboldunderlord]

Hive handles primitive types using the base Hadoop writable rather than its own during joins, which means that in order to use the proper DoubleWritable class from Hive you have to actually return an object of the appropriate type in JsonSerDe.serializeField instead of a primitive.

[koboldunderlord]

Closing this out & reopening using valueOf for objects to allow Java to optimize object creation better