An implementation of <Improved boosting algorithms using confidence-rated predictions>, Schapire, 1999
##class Adaboost Basic Adaboost to solve two-class problem
##class AdaboostMH Adaboost that could solve multi-class and multi-label problem.
##class AdaboostMO A multi-class version of Adaboost based on output codes to solve single-label problem