* use hook instead of invoke so it's easy to configure
* hook into controller_generator and scaffold_controller_generator
This feels more natural than invoking from the resource generator.
Decorators are closely related to controllers, views and helpers.
So they should be generated in that context.
If controller generation is disabled for say generating resources there
is no point in creating decorators.
* Use the new `expect().to` syntax
* Avoid general fixtures by minimizing usage of `let` and `subject`
* Define as few support classes as possible, and use them for name
lookup only - all behavior is introduced by stubbing
Lots of changes here:
* rake draper:install no longer needed
* don't generate an ApplicationGenerator by default
** If one exists, the generator respects it
* Fixes#53
