Function vecRotate

vecRotate(a: Vec2, angle: number, around: Vec2): Vec2
Rotate a vector counterclockwise around a pivot point
Parameters
- a: Vec2
  vector to rotate
- angle: number
  angle in radians
- around: Vec2
  pivot point
Returns Vec2
rotated vector
Example
```
vecRotate([1, 1], Math.PI, [0, 0]);   // returns [-1, -1]
```
- Defined in vector.ts:71