Don't assume ojects in data store get indifferent access.
Store objects in a Hash without serializing them.

* Change internal storage from Array to Hash.
  * Makes it easier to find by ID.
* Don't serialize objects - just store copies of them in the Hash.
* Set ID for Hash-like objects and other objects.
* Don't make object keys indifferent.
* Refactor the way we determine and set IDs.
Register the adapter with Perpetuity.
Update README with some TODO items.
Add integration test.
Bump version to 0.2.0.