Webber, Chapter 13, Exercise 10.
DUE WEDNESDAY, FEB. 24TH. Submit your java files to inquire by the beginning of class.
  Write a class in Java called Fraction, which represents
  a generic fraction object.  Towards that end, you must have:
add(otherFraction),
    sub(otherFraction),
    mul(otherFraction),
    and div(otherFraction).  These should return a new
    Fraction object, as opposed to modifying the current fraction
    object.
  Create a program you can use to test your program. Make sure you test all of the methods of your classes.