fixes test_add_factors, adds test_get_factors in MarkovModel
fixes test_add_factors, adds test_get_factors in MarkovModel

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