Supports union completion in structs - #86

Light :: struct {
    type: LightType;
    union {
        point: struct {
            position: Vec3f;
            color: Vec3f;
            intensity: float;
            range: float;
        }
        spot: struct {
            position: Vec3f;
            color: Vec3f;
            intensity: float;
            range: float;
            direction: Vec3f;
            inner_cone: float;
            outer_cone: float;
        }
    }
}