GitLab

* first update

* update by folder naming

* add gradient feature selection example

* add examples

* delete unused example

* update by pylint

* update by pylint

* update learnability by info from pylint

* fix pylint in fgtrain

* update fginitlize and learnability by pylint

* update by evan's response

* add gbdt_selector

* update gbdt_selector

* refine the example folder structure

* update feature engineering doc

* update docs of feature selector

* update doc of gradientfeature selector

* update docs of GBDTSelector

* update examples of gradientfeature selector

* update folder structure

* update docs by folder structure

* test pylint

* test

* update by pylint

* update by pylint

* update docs and remove some dependency

* remove unused code

* update by comments

* update by comments

* move the feature selection example path

* delete unused dependency