Discretizer for Real valued features

We should support discretization techniques for Real valued feature into discrete values. This would help when we have mixed discrete/real features in our experiments.

One reference that is popularly used: MDL Discretizer 
http://www.decom.ufop.br/luiz/site_media/uploads/arquivos/bcc444_pcc142/multiintervaldiscretizationofcontinuousvaluedattributesforclassificationlearning1993.pdf
