Change XGBoost to GBDT?

[javicarron]

Currently, one of the ML methods in the dictionary is XGBoost (eXtreme Gradient Boosting).
This is the name of a package that implements Gradient Boosting techniques (also called Gradient Boosting Decision Trees). Although this is the most famous package for this techniques, it is not the only one, so I would propose to change it to Gradient Boosting or Gradient Boosting Decision Trees to focus on the technique more than the implementation.

In any case, this is not very important, so feel free to close the issue if you don't agree.

Also, thanks for the nice compilation of interesting papers!