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

issue: https://jira.kiji.org/browse/EXP-403
review: https://review.kiji.org/r/1573
commit: https://github.com/kijiproject/kiji-modeling/commit/49feffcb0709098e3a9f17a285f186c4aa303355