Example
-----
    myWheel := wheel.New()
    err := myWheel.AddValue(0.60, "60% chance A")
    if err != nil {
        log.Fatal(err)
    }
    err = myWheel.AddValue(0.40, "40% chance B")
    if err != nil {
        log.Fatal(err)
    }

    randomValue := myWheel.Spin()