Update to rspec 3 and modern "expect" syntax.

- Expect syntax is now the default in rspec, do that conversion.
- Utilize implicit subject.
- Avoid expect(x).to include(z) because it doesn't work the way we
  want for lists; stick with true/false assertions.
Merge pull request #36 from kylev/kv_spec_update

Update to rspec 3 and modern "expect" syntax.