[refs #174] Changes in Markov Model class and tests
Merge remote-tracking branch 'origin/issue174' into issue174

Conflicts:
	pgmpy/Factor/Factor.py
Update .travis.yml
Update .travis.yml
Merge pull request #195 from ankurankan/issue174

Issue174
Merge pull request #193 from ankurankan/dev

Bayesian Model Tests
Merge remote-tracking branch 'upstream/dev' into issue/196
[refs #196] commented out because incomplete and was giving syntax error