Exercise 8-1

In the Item class:
1. Declare a setColor method that takes a char as an argument (a color code)
     and returns a boolean.
     Return false if the colorCode is ' '.
     Otherwise, assign the colorCode to the color field and return true.

In the ShoppingCart class:
2. Call the setColor method on item1.  If it returns true,
     print out item1.color.  If it returns false, print an
     invalid color message.
3. Test the method with both a valid color and an invalid one.