CartProcessor can return Cart List and test pass
modify ItemProcessor file and test
modify ItemProcessot.java
modify Promotion constructer
add PromotionProcessorTest.java
add PromotionProcessor can return an promotion list with one parament test and file
add PromotionProcessor can return an promotion list with two parament test and file
add a private process function in PromotionProcessor  and test pass
add a halfProcess and freeProcess  in PromotionProcessor and test pass
modify promotion.java
finish discountProcess in PromotionProcessor and test pass