administrate 0.20.0

Administrate is heavily inspired by projects like Rails Admin and ActiveAdmin, but aims to provide a better user experience for site admins, and to be easier for developers to customize. To do that, we're following a few simple rules: - No DSLs (domain-specific languages) - Support the simplest use cases, and let the user override defaults with standard tools such as plain Rails controllers and views. - Break up the library into core components and plugins, so each component stays small and easy to maintain.