add callback after created controller.

Sometimes view controller has a data.
The controller was set as a root view controller to the window before called "before" block.
But a data is not set at this point.
The view controller access to nil, and crash sometime even if I set a data in "before" block.

After created controller it will call the specified callback method if you set :after_created option

# Example
  describe MyViewController do

    tests MyViewController, after_created: :after_created_controller

    def after_created_controller controller
      # you can set data to the controller here
      controller.my_data = "foo"
    end

    .
    .
  end
Merge pull request #96 from katsuyoshi/callback_setup_controller

add callback after created controller.