Implement 'safe' mod operator for Point-like types

[davesmith00000]

By safe I mean a version that works with negative numbers. Applies to Point, Vertex, Vector2/3/4.

[davesmith00000]

~Math.floorMod may be the thing these days, rather than the old (((-1 % 2) + 2) % 2), business.~ floorMod doesn't work with doubles.

We're back to (number % divisor + divisor) % divisor.

[davesmith00000]

Implemented for Point, Radians, Size, Vertex, Vector 2/3/4.