add default vector implementation

As requested by sk89q in <https://github.com/SpongePowered/Sponge/pull/29>.
This method should compare each element, shouldn't it?
Example:
a > c
a + b > c + b (FAILs if b = -a)
|(1 1)|² > |(0 0)|² <=> 2 > 0
|(1 1) + (-1 -1)|² < |(0 0) + (-1 -1)|² <=> 0 < 2
But I'm not sure whether this is required by `Comparable`