Improvements in file structure

- File structure is great but I would separate model.js into 3 files: delete-user.model.js ,get-users.model.js, add-new-user.model.js → create models folder → add them there and move the folder into your root of the project. If you do that do not forget to change require path in your handlers.
 
Model: 
- models
   - get-users.model.js
   - add-new-user.model.js
   - delete-user.model.js