Deploy a new doc website (#338)

A new documentation website. And:

* add actions for doc

* update docstr

* installation instructions for doc dev

* unify README and Getting Started

* rename notebook

* doc about best_model_for_estimator #340

* docstr for keep_search_state #340

* DNN

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>
Co-authored-by: Z.sk <shaokunzhang@psu.edu>