Improving Markov Model's code pulled from navin [refs #174]
Fixed MarkovModel [refs #174]
methods left: _norm_h, normalization_constant_brute_force, make_jt
adds triangulate method for markov models [refs #174]
adds attribute cardinality to markov models [refs #177]
adds 6 heuristic methods for computing traingulated graph [refs #174]
minor changes
Implements induced_graph for Markov Models [refs #174, fixes #186]
Merge branch 'dev' into issue174

Conflicts:
	pgmpy/Factor/Factor.py
Merge pull request #175 from ankurankan/issue174

Issue174