Add more coloring options -- bicoloring

[amontoison]

I suggest to add a function for acyclic coloring, which is relerant for Hessian coloring.

cc @gdalle

[gdalle]

In the meantime, SparseMatrixColorings has evolved to be a much richer interface than can be provided by ADTypes, so I doubt adding new names here would help much. Closing this for now if that's okay :)

[amontoison]

Maybe we can add bicoloring? I think that the variants star / acyclic should a be a kwarg of symmetric_coloring and bicoloring.