Quick overview of variables of importance, ranked according to contribution.

## [14:55:54] WARNING: src/learner.cc:553: 
##   If you are loading a serialized model (like pickle in Python, RDS in R) generated by
##   older XGBoost, please export the model by calling `Booster.save_model` from that version
##   first, then load it back in current version. See:
## 
##     https://xgboost.readthedocs.io/en/latest/tutorials/saving_model.html
## 
##   for more details about differences between saving model and serializing.
## [14:55:54] WARNING: src/learner.cc:553: 
##   If you are loading a serialized model (like pickle in Python, RDS in R) generated by
##   older XGBoost, please export the model by calling `Booster.save_model` from that version
##   first, then load it back in current version. See:
## 
##     https://xgboost.readthedocs.io/en/latest/tutorials/saving_model.html
## 
##   for more details about differences between saving model and serializing.
## [14:55:54] WARNING: src/learner.cc:553: 
##   If you are loading a serialized model (like pickle in Python, RDS in R) generated by
##   older XGBoost, please export the model by calling `Booster.save_model` from that version
##   first, then load it back in current version. See:
## 
##     https://xgboost.readthedocs.io/en/latest/tutorials/saving_model.html
## 
##   for more details about differences between saving model and serializing.