[2pt] - Create the Author class

[laiifuu]

• Create an Author class with an association to the Item class (in a separate .rb file).
• All Author class properties visible in the diagram should be defined and set up in the constructor method.
• Implement method:
  • add_item method in the Author class:
    • should take an instance of the Item class as an input
    • should add the input item to the collection of items
    • should add self as a property of the item object (by using the correct setter from the item object)