Start work on a Shopping Cart
Build initial ShoppingCart class
Ability to add products to the shopping cart
That's some bad math there
Add a test for scope
Add initial function functionality with a dummy function
Add buy_two_get_one_free function
Add final function, restructure how functions are added

The final function requires some more abstract data, which means that the final functions have to be restructured to allow a key of arguments.

Also added a way to represent the cart, which shows the total and the content.