Add unit tests for `express-annotations`

- Brings coverage to near 100%
- Switches testing-style to BDD `expect`-style as
  with the other Modown components
Increase `express-annotations` coverage to 100%

- Add remaining test for non-string Error
- Add miscellaneous tests to check for correct route objects
Merge pull request #7 from clarle/annotations-tests

Increase `express-annotations` coverage to 100%