Vector.opUnary

const v1 = Vector2I(2, -5);
assert((+v1).v == [2, -5]);
assert((-v1).v == [-2, 5]);
assert((~v1).v == [-3, 4]);
// *** BUG ***
//auto v2 = Vector!(bool, 2)(true, false);
//assert((!v2).v == [false, true]);