Refactored so Monomial and FractionMonomial are PolyUnit and FracPolyUnit (so as not to be confused with the mathematical concept of a monomial).
Removed divide(PolyUnit) from Polynomial (both) because it had no apparent use.
Refactored Fraction.testIfInt() to Fraction.isInt().
Implemented reduction of Irrationals to smallest possible radicand.
Refactored Irrational to be Radical (since the class is meant to deal with radicals, specifically, and not irrationals like tau, e, etc.).
Implemented addition and subtraction of Radicals.