Function nalgebra_glm::faceforward

pub fn faceforward<N: Number, D: Dimension>(
    n: &TVec<N, D>, 
    i: &TVec<N, D>, 
    nref: &TVec<N, D>
) -> TVec<N, D> where
    DefaultAllocator: Alloc<N, D>, 

If dot(nref, i) < 0.0, return n, otherwise, return -n.