feature request: isZeroLength for Vector

[ensconced]

Segment has an isZeroLength method - would it make sense to add the same for Vector?

Of couse I can do vec.length === 0, but this involves an expensive Math.sqrt. I can do vec.dot(vec) === 0 to avoid the sqrt, but this somewhat less readable.

[ensconced]

Alternatively, maybe we could have a lengthSquared method - that would also serve cases where vectors need to be compared by length, and the overhead of the sqrt is not necessary