git move the users_controller to the proper /api/v1 path for version control;
rename the namespace of users_controller;
update create and create_user_params methods to make use of strong parameter for users_controller;
(1) update update and update_user_params methods to make use of strong parameter for users_controller;
(2) update update and destroy methods with new respond_to method;
update index and show methods with new respond_to method;
add model for api_key;