code: function Rot(angle) {
    if (!(this instanceof Rot)) {
      return new Rot(angle);
    }
    if (typeof angle === 'number') {
      this.setAngle(angle);
    } else if (typeof angle === 'object') {
        this.set(angle);
    } else {
      this.setIdentity();
    }
  }
docs: TODO merge with Transform 
  Initialize from an angle in radians.