dot(), selector() and other 'abstracted tools' for dealing with Python dict keys

Python, unlike json, can have any hashable object as a key in it's dicts.  If we want to expand from jsonable data to general Simple Data Structures (SDS), then we need ways of dealing with them in selectors.
## Proposal
- `dot()`
- `selector()` 

and other classes that are slightly more abstract.
