Latest version of 0.2x

This is latest version of 0.2x, used to document before changing the code into xgboost-unity

Second release, with BugFix

Fix a major bug in v0.2 #8 and #10 .
scale_pos_weight is not properly initialized to default.
The bug will cause binary classification model work improperly when scale_pos_weight is not set in the parameter.

But if the scale_pos_weight is set properly, the result will be correct in v0.2

first release

XGBoost with regression and binary classification support