Parable ORM 0.6.0

0.6.0

And we're back to no casting whatsoever. 0.5.0 was intended to be a first step to more complete type casting for values, but it became clear the functionality wasn't going where it needed to go.

So, placing the responsibility back at the implementation where I now believe it lies. The other improvements from 0.5.0 have been kept, however.