remove notice in doc about in-development feature
Several fixes to make to and from json conversion possible

- support triple quote strings with double quote included in it
- isinstance takes also an empty JSObject as second argument
- moved json_to_pythonjs and created pythonjs_to_json in builtins.py
Several fixes

- Missing JSObjects in __getattr__ overriding code
- Fixed *args, **kwargs handling in calling code
- Added dict.pop
- Fixed json_to_pythonjs
- Fixed python_to_rpythonjs command