function transformMat4(out, a, m) {
    var x = a[0], y = a[1], z = a[2],
        w = m[3] * x + m[7] * y + m[11] * z + m[15]
    w = w || 1.0
    out[0] = (m[0] * x + m[4] * y + m[8] * z + m[12]) / w
    out[1] = (m[1] * x + m[5] * y + m[9] * z + m[13]) / w
    out[2] = (m[2] * x + m[6] * y + m[10] * z + m[14]) / w
    return out
}
Transforms the vec3 with a mat4.
4th vector component is implicitly '1'

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