Recursive function that returns a node structure under the MediBoost paradigm
likelihoodMediboostSplitNode(x, y, weights, catPredictors, obsValues,
nodeValue, colIdx, depth, depthLimit, learningRate, gamma, membership,
min.membership, steps.past.min.membership, min.mem.counter, update,
min.update = ifelse(update == "exponential", 1000, 10), hessian,
min.hessian, save.rpart, verbose = TRUE)