Fix line lengths in documentation and lint *.book files as JSON.
Summary: Fix a few "line too long" lint issues in the Diviner documentation. Also lint *.book files as JSON.
Test Plan: Eye-ball it.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9695