Add maximum depth limit to ladder features.
Add maximum depth limit to ladder features.

Rochester-NRT/AlphaGo,Rochester-NRT/RocAlphaGo,hiropppe/RocAlphaGo,Rochester-NRT/AlphaGo,Rochester-NRT/AlphaGo,wrongu/RocAlphaGo,MaMiFreak/RocAlphaGo,vftens/RocAlphaGo