Vector2/3/4 + Quaternion Optimizations

- variable reuse (less mem, faster attribution - http://jsperf.com/pro-var-reuse);
- `undefined` replaced by `void(0)`, since is slight faster, value safe and uses less chars (http://jsperf.com/typeof-vs-undefined-check/22);
- `<Vector2/3/4>.roundToZero()` ceils negatives and floors positives using a simple `n |= 0`;
- using `*= -1` to negate properties (better minification, http://jsperf.com/fast-negate-numeric-property);
- multiply is faster than divide (http://jsperf.com/multiply-vs-divide/3) ex: `n / 2` to `n * 0.5` and `n / 4` to `n * 0.25`;
- minor optimizations.