Build tests around intended semantic equivalencies

[vreuter]

A core tenet of this package is equivalence--for various operations--between dot notation / attribute-style syntax and key / __getitem__ syntax. Some testing to this effect is already in place, but it should be more thorough, both for automated assurance of full functionality, and as a sort of in-code specification of the package's capabilities. Furthermore, building around this tenet emphasizes its centrality to the package's purpose.

• Membership (in, hasattr)
• Fetch ([], ., getattr, get)
• Set (., [], update, setdefault, setattr)