Added setter and getter for the numerator and denominator

[LarryBattle]

Added setter and getter for the numerator and denominator. Also change this.numerator to this.n and this.denominator to this.d. This should also includes the parameter names. top-> n and bottom -> d

Ratio.js

numerator : function(val){
    if(val != null){
        this.n = Ratio.getNumeratorWithSign(val, this.d);
    }
    return this.n;
},
denominator : function(val){
    if(val != null){
        this.n *= (0 < +val) ? 1 : -1;
        this.d = Math.abs(val);
    }
    return this.d;
},

Test cases

test("test Ratio.prototype.numerator()", function () {
    var fn = function(a,b,c){
        var obj = new Ratio(a,b);
        obj.numerator(c);
        return obj;
    };
    equal(fn(1,2,2).toString(), "2/2");
});
test("test changing denominator", function () {
    var fn = function(a,b,c){
        var obj = new Ratio(a,b);
        obj.denominator(c);
        return obj;
    };
    equal(fn(1,3,2).toString(), "1/2");
    equal(fn(-1,3,-2).toString(), "1/2");
    equal(fn(1,3,-2).toString(), "-1/2");
    equal(fn(-1,3,2).toString(), "-1/2");
});

[LarryBattle]

Added in Version 0.4