Add hierarchy to Tuples

[bmccutchon]

I've added a hierarchy for Tuples in my fork. The hierarchy looks like this:

• Tuple
  • Tupled
    • Tuple2d, Tuple3d, Tuple4d
  • Tuplef
    • Tuple2f, Tuple3f, Tuple4f
  • Tuplei
    • Tuple2i, Tuple3i, Tuple4i

Tupleb is missing from this because the Tuple*b classes don't currently have many of the methods that other Tuples do. The upper-level classes in this hierarchy declare useful abstract methods, so that it is possible to write code like this:

    // Average method for Tuples of type double
    @SafeVarargs
    public static <T extends Tupled<T>> T average(Tuple<T>... tuples) {
        T avg = sum(tuples);
        avg.scale(1.0 / ((double) tuples.length));
        return avg;
    }

    // Sum method for all Tuples (besides those of type byte)
    @SuppressWarnings("unchecked")
    @SafeVarargs
    public static <T extends Tuple<T>> T sum(Tuple<T>... tuples) {
        T sum = (T) tuples[0].clone();
        for (int i = 1; i < tuples.length; i++) {
            sum.add((T) tuples[i]);
        }
        return sum;
    }

This resolves #3.