Update Book model

- no longer a Postable
- new fields for reading start and end dates
Add comments to posts#show
Use .present?, not .any? to check for array items
New books#index
Nicer _book partial and renamed authors helper
More specific nav_link_to…

`controller_path` instead of `controller_name`
includes the namespace, so `meta/pages` isn't
treated the same as `pages`
New routes (with redirects from old ones)

...but removes static redirects that can be put
in the database. Also, helpful hints for redirect
fields.
Add expires headers for assets
Remove trailing slashes with middleware
Cuter 422.html
Fix static asset caching