function transformMat3(out, a, m) {
    var x = a[0], y = a[1], z = a[2]
    out[0] = x * m[0] + y * m[3] + z * m[6]
    out[1] = x * m[1] + y * m[4] + z * m[7]
    out[2] = x * m[2] + y * m[5] + z * m[8]
    return out
}
Transforms the vec3 with a mat3.

@param {vec3} out the receiving vector
@param {vec3} a the vector to transform
@param {mat4} m the 3x3 matrix to transform with
@returns {vec3} out