A Stock Item


Design a class named StockItem that can be used to keep track of items in stock
 at a store. Each stock item object must include the following:

 the item name
 a price 
 the quantity of the item that is currently in stock

When a StockItem object is created, the object must be constructed with a 
name, a price, and a current quantity.  (only 1 constructor)


Operations on a stock item include the 
following:

 retrieve the description of the item
 retrieve the price of the item
 retrieve the quantity of the item that is currently in stock
 set a new price for the item
 remove some quantity of the item from the quantity in stock
 add some quantity of the item to the quantity in stock

Write the StockItem class