Fixes #6: naked expect(N) behaves like QUnit.expect(N)
Merge remote-tracking branch 'machty/qunit-expect'

* machty/qunit-expect:
  Fixes #6: naked expect(N) behaves like QUnit.expect(N)
Tidy up after merging #6.

- Add a note to the README saying `expect(4)` should still work as expected.
- Consolidate the getting and setting of `_previousExpectedAssertions`.
- Remove a branch from `expect.configure()` that checked for `Object.defineProperty` since we already depend on it to exist.
v0.3.0