WIP Multilabel model

This is a work-in-progress on multilabel prediction with label correlations.
This is a standard example in many structured prediction papers, so I think it would be nice to have it, if only to compare to the literature.
Basically the multi-label model is a densely connected pairwise crf with binary nodes.

I also have some code there for constructing a chow-liu-tree, which is the best tree-model for a given set of inputs.
That would be a nice comparison, as it is much simpler from an inference point of view.