kiji-express: EXP-155. Ensure all packages have documented package objects.

issue: https://jira.kiji.org/browse/EXP-155
review: https://review.kiji.org/r/1374
commit: https://github.com/kijiproject/kiji-express/commit/35f4e9aafe167b73b045b3f46778fafa8942211f