xgboost_ray-0.1.3

• Support for more data sources: Ray datasets and general improvements (#139, #140, #141, #145)
• Placement group fixes (#136, #143)
• Usability improvements (#148, #149)
• Various minor fixes/updates (#137, #144, #150, #154)
• xgboost is now an extra dependency (and might have to be installed separately) (#151)