#s 57 and 58, with update to useful.py

useful.py and 57.py both include my new fraction class. It does it all!

Here's all the things you can do with my fraction datatype:
-create a fraction, with default values of one for both numerator and
denominator, ordered such that if you call Fraction() with a whole
number, it creates the fraction [whole number]/1
-add two fractions using +
-subtract two fractions using -
-multiply two fractions using *
-divide two fractions using /
-invert a fraction
-reduce a fraction to lowest terms
-print a fraction using the standard "print" command and get what you
expect, eg. "a/b"