Implement AR.
Implement a Rack app & middleware.
Implement Front controller.
Implement UsersController and routing DSL.
Implement Intercepting filter.
Implement around filters.
Implement ERB view rendering.
Implement implicit rendering.
Make test pass.
Rename active_record file to not_active_record.

To prevent clash w/ real active_record lib.
Use ActiveSupport in Filters.
Add validation to our user model.