LightGBM

Use one-vs-other for small categorical features.

commit c9e123f24fcbb159c04e6694c7f830530bb2f27e
Author: Guolin Ke <i@yumumu.me>
Date:   Wed Oct 18 10:00:19 2017 +0800

    change default max_cat_to_onehot

commit 805a5c3125b9979d634922e1708877fa0fec80c6
Author: Guolin Ke <i@yumumu.me>
Date:   Tue Oct 17 22:57:18 2017 +0800

    use one hot coding for the small cats