kiji-express: EXP-403. Scaladoc cleanup for *Spec classes.

issue: https://jira.kiji.org/browse/EXP-403
review: https://review.kiji.org/r/1571
commit: https://github.com/kijiproject/kiji-express/commit/5c62b4d48900adc95d8ada5052b3fa3409202b25