Issue #58 update: equals() for MathFunction

Added an equals() function and a generic hashCode() function to the MathFunction class, (both were basically auto-generated from the Eclipse tools, I just changed the format a bit to line up with the Term equals function).
Did some quick testing and it appears to work since the termsByExponent TreeMap container is essentially calling equals on all keys and values (using Set equals).  Should I write a unit test for it before this is reviewed?