https://arxiv.org/pdf/1603.02754v3.pdf
http://xgboost.readthedocs.io/en/latest/python/python_api.html
http://xgboost.readthedocs.io/en/latest/python/python_intro.html
http://www.slideshare.net/ShangxuanZhang/winning-data-science-competitions-presented-by-owen-zhang
http://www.machinelearning.ru/wiki/images/5/56/Guschin2015Stacking.pdf
http://mlwave.com/kaggle-ensembling-guide/
https://github.com/bamine/Kaggle-stuff/blob/master/otto/hyperopt_xgboost.py