Consider adding Additive Groves

[eandrejko]

It would be interesting to add support for additive grove models and make this a more general library for ensembles of decision trees.

http://www.ccs.neu.edu/home/mirek/papers/2007-ECML-Groves.pdf

Another method of interest for some types of problems would be Oblique Random Forests:

http://people.csail.mit.edu/menze/papers/menze_11_oblique.pdf