add un_balance to multi class (#314)
add un_balance to multi class (#314)

* add un_balance to multi class

* change the calculation of label weights

microsoft/LightGBM,huanzhang12/lightgbm-gpu,huanzhang12/lightgbm-gpu,sightmachine/LightGBM,sightmachine/LightGBM,olofer/LightGBM,Allardvm/LightGBM,olofer/LightGBM,huanzhang12/LightGBM,Laurae2/LightGBM,fstonezst/LightGBM,huanzhang12/LightGBM,Allardvm/LightGBM,fstonezst/LightGBM,henry0312/LightGBM,Laurae2/LightGBM,olofer/LightGBM,huanzhang12/lightgbm-gpu,microsoft/LightGBM,wxchan/LightGBM,Allardvm/LightGBM,Allardvm/LightGBM,microsoft/LightGBM,microsoft/LightGBM,huanzhang12/lightgbm-gpu,henry0312/LightGBM,huanzhang12/LightGBM,Laurae2/LightGBM,wxchan/LightGBM,henry0312/LightGBM,olofer/LightGBM,henry0312/LightGBM,sightmachine/LightGBM,fstonezst/LightGBM,huanzhang12/LightGBM,wxchan/LightGBM,fstonezst/LightGBM,Laurae2/LightGBM,olofer/LightGBM,henry0312/LightGBM,wxchan/LightGBM,huanzhang12/LightGBM,sightmachine/LightGBM,Allardvm/LightGBM,wxchan/LightGBM,fstonezst/LightGBM,huanzhang12/lightgbm-gpu,Laurae2/LightGBM,microsoft/LightGBM