Add neccesary class files and test files.
  *Create testcase inside test.file
  *Create getter,setter, initialize, and depreciated_value methods.
Modify Depreciated_value method
Updade data set for test.rb. Add mark_up class, car.rb.
Modify Car.rb, Add Usedcar.rb and test_usedcar.rb
  *usedcar.rb - Add mileage as new argument. Add mileage calculation method.
Add carlot class and damage class. Unfinished.
Add carlot.rb class. Method Lot_value_calc.