0.6: Fix unexpected behavior with optional values (#19)

* Add hash-tables to sanity-clause.util:get-value

They're a major associative data structure and deserve to be there, too.

* Update readme

* Fix quote attribution
* Fix loadable schema function name
* A typo or two

* Make test descriptions for one-of fields clearer

Because I was confused about what they did, today.

* Reference `resolve` method correctly

Fixes some style warnings I hadn't noticed before

* Make classes use same protocol as plist schemas

This closes the loop on differences in behavior between the two types
of schemas, eg. allowing :missing values for non-required fields.

* Fix nested schemas/clarify limitations in docs

* Make license a real license

* Version bump

* Docs

* Use `resolve` from the protocol package

* Turns out, ccl is stricter about slot types than sbcl