Add User stories

- Create a car
- Add car to lot
- moved User Stories.txt from features into the main folder
Add 2 User stories

- Look up car by ID
- Look up number of cars in lot
Moved user_stories.txt from features into main project folder.
Add User story - create used cars

- Add used_car class
Add User Story - look up sales price

- can be done with a manual price adjustment
Add User Story - add damage to cars

- Add damage to cars
- Create damage class
- Determine damage value based on whether it is fixed
Update car_lot_management_app.rb