https://www.kaggle.com/c/mercari-price-suggestion-challenge/
https://github.com/pjankiewicz/mercari-solution/raw/master/presentation/build/yandex.pdf
merge_predictions =
-0.0203
0.0604 * data1_huber
0.1051 * data1_huber
0.0911 * data1_clf
0.0760 * data1_clf
0.0851 * data2_huber_bin
0.0981 * data2_huber
0.0819 * data2_clf_bin
0.0717 * data2_clf
0.0958 * data3_huber_bin
0.1226 * data3_huber
0.0578 * data3_clf_bin
0.0642 * data3_clf
=> RMSLE 0.3733