Add link functions for common glm models

[MaxBenChrist]

Now vikos is able to fit arbitrary glm models.

It would be nice if one adds the link functions for custom glm models such as Normal, Exponential, and so on.

You can find an overview here: Table custom link functions

[pacman82]

What would be the benefit of supporting these models through GLM + link function rather than through a newtype pattern of Linear (e.g. pub struct Logistic<V: Vector>(Linear<V>);)?