Added date to the receipt, and tests for that initialization
Added docstrings to all of the classes. Refactored the shop module name to receipts and the GroceryStore class to Store.
Added methods to Receipt and Item. Added missing variable to Item class. Created tests for the initialization on the Item class.
Added 2 methods. One to add items to a receipt and a magic method str() to the Item class.
Added a test for the srt() addition