Vec2 and Vec3 child classes

[LucaCiucci]

I was wondering if it was a good idea to add some specialized sub classes to provide more strict requirements, something like:

class Vec2 extends Vec {
    constructor(x : number = 0, y : number = 0) {
        super(x, y);
    }
    // ...
}

The library should continue to work without any major modification.

[learosema]

Good point.