Summary: I want to allow a single project to generate multiple "books" of documentation, so we can separate user-facing documentation from technical documentation and such. Generalize the ".divinerconfig" file into a "diviner book" configuration file. Since only the "generate" workflow actually reads any of this stuff, move it all down into the generate workflow. Also, namespace the cache. Test Plan: Ran `bin/diviner generate --book src/docs/user.book`, saw appropriate output. Verified cache generated in a namespace in `.divinercache/`. Reviewers: btrahan, indiefan Reviewed By: btrahan CC: aran Maniphest Tasks: T988 Differential Revision: https://secure.phabricator.com/D4857