small fixes

[stokito]

Here is small changes with cleanup and small fixes. But I have an additional question: In the 1ca1602 commit I changed body of the RoundedMoney.isZero() so now it looks exactly the same as in javax.money.MonetaryAmount#isZero. In the MonetaryAmount are declared such methods:

    public boolean isZero() {
        return signum() == 0;
    }

    public boolean isPositive() {
        return signum() == 1;
    }

    public boolean isPositiveOrZero() {
        return signum() >= 0;
    }

    public boolean isNegative() {
        return signum() == -1;
    }

    public boolean isNegativeOrZero() {
        return signum() <= 0;
    }

And all of them with exactly the same body are declared in Money and RoundingMoney. So maybe we can just remove the isZero, isPositive etc methods from the Money and RoundingMoney?

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