predictor visibility in AnchorTabular

[RobertSamoilescu]

• Consider changing the visibility of predictor from public to private, and update the documentation examples. Instead of using the explainer.predictor, use directly the original predictor.

• The predictor is set to None when saving:
  

  alibi/alibi/saving.py

  Lines 101 to 106 in af1b351

  	def _simple_save(explainer: 'Explainer', path: Union[str, os.PathLike]) -> None:
  	predictor = explainer.predictor # type: ignore
  	explainer.predictor = None # type: ignore
  	with open(Path(path, 'explainer.dill'), 'wb') as f:
  	dill.dump(explainer, f, recurse=True)
  	explainer.predictor = predictor # type: ignore

• Specify that in order to change the predictor, reset_predictor should be called.

[jklaise]

This extends to all explainers. Will need to check if some other projects (Core, Tempo) are using the predictor attribute directly @cliveseldon .