Kaggle playground
- https://www.kaggle.com/arthurtok/introduction-to-ensembling-stacking-in-python
- https://www.kaggle.com/general/18793
- https://www.kaggle.com/mmueller/allstate-claims-severity/stacking-starter/run/390867
- https://mlwave.com/kaggle-ensembling-guide/
- https://github.com/emanuele/kaggle_pbr/blob/master/blend.py