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
Minor changes in _bivar_factor_product
factor product
changes in __str__ of Factor
Merge pull request #179 from ankurankan/dev

Factor Product and __str__ of Factor
fixed factor product for factors with common variables [refs #172]
[fixes #172] fixes factor product for factor with no common variable
Merge pull request #181 from ankurankan/dev

Fixes Factor Product
Improved __str__ method of factor
Merge pull request #185 from ankurankan/dev

Improved __str__ method of factor
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
- Modified .travis.yml and setup.py for error-free continous integration
- Added continous_integration/install.sh for easier installation of
  dependencies