Testing examples

[stuartpb]

I just checked and I'm pretty sure the examples listed for v0.1 and v0.2 are invalid.

While the fixes involved to address this should be minor, the fact remains that each schema should be tested against its example profiles / legacies.

[stuartpb]

#24 hits another kind of example that isn't tested against - the excerpts in Markdown documentation. I'm not sure how to structure these to be testable without being way too invasive about YAML blocks in documentation, but it's something to consider.

[stuartpb]

As an example of the kind of thing that would be caught by these tests, https://github.com/opws/opws-schemata/blob/82799027df007c5d0002aecb11762de891eeac3d/v0.2/examples/exhaustive.yaml has a root "terms" object for what would now go under legal.documents.

I'm going to hold off on filing issues for these kinds of discrepancies, in favor of this one that will catch all these issues once implemented (though, TBH, I should just be making fixes as I notice them).