added get_cardinality method in MarkovModel
added get_cardinality method in MarkovModel

sandeepkrjha/pgmpy,yashu-seth/pgmpy,ankurankan/pgmpy,anaviltripathi/pgmpy,yashu-seth/pgmpy,pgmpy/pgmpy,anaviltripathi/pgmpy,abinashpanda/pgmpy,jhonatanoliveira/pgmpy,abinashpanda/pgmpy,kris-singh/pgmpy,khalibartan/pgmpy,khalibartan/pgmpy,ankurankan/pgmpy,jhonatanoliveira/pgmpy,pgmpy/pgmpy,liquidmetal/pgmpy,liquidmetal/pgmpy,sandeepkrjha/pgmpy,kris-singh/pgmpy