Inheriting from PyOnJs will add a dumps to instances, and loads to the class.
    instance.dumps() dumps out to a json string, where Klass.loads(...) will return an
    instance of Klass initialized from the string. Only works in Python 3.


    Internally this relies upon the default json library in python. What it adds is the
    ability for classes to define _json and _jsonc attributes to control the saving and
    loading of attributes. Only the top level to extends PyOnJs, but all levels need 
    have _json and _jsonc.

    _json must be a list of the names of attributes that will be serialized.

    _jsonc is an optional dictionary that maps property names to the types that they
    should be. The types can either be a single class, or a list for custom types nested
    inside lists or dictionaries.  At this point dictionaries can only be strings to
    other types. For example: [list, dict, Klass] would be interpreted as a list of
    dicts that map from strings to instances of Klass.

    If any attributes are missing from an object being de-serialized, an exception will
    be thrown.