0.2.4

Features

• Discard hessian splits with score lower than the parents. This change has
  little effect on the model quality, but it can reduce its size.
• Add internal flag hessian_split_score_subtract_parent to subtract the
  parent score in the computation of an hessian split score.
• Add the hyper-parameter optimizer as one of the meta-learner.
• The Random Forest and CART learners support the NUMERICAL_UPLIFT task.