Move to specta/specta, specta/expecta, and XCTest

1 test was failing for me before and is still failing for me.

The tests depended on an addition to github/specta that allowed a cleanup phase to run after every example. Since specta/specta doesn't have this, I added a `afterEach(^{ [self tearDown]; })` to the bottom of each spec. It's not pretty, but it works.
Yes. The forks were true forks and had diverged. Instead of keeping the forks up to date, I'm switching everything to the upstream.