Add a JSONPojoConvertor and enhance JSONObjectConvertor to do caching.
- Converts POJOs to JSON and vice versa.
- The key difference:
- - returns the actual object from Convertor.fromJSON (JSONObjectConverter returns a Map)
- - the getters/setters are resolved at initialization (JSONObjectConverter resolves it at runtime)
- - correctly sets the number fields
The JSONObjectConvertor could act as the default convertor and act as a cache of pojo convertors.