issue-65 PomdpXReader Class r=ankurankan
added the test pomdpx xml file
PomdpX Reader Class
Merge branch 'dev' of https://github.com/pgmpy/pgmpy into pomdpX
minor changes
minor changes - pep8 issues, pythonic code, removed test file.
added methods and tests to support Decision Diagram parameter format
Merge pull request #168 from ankurankan/dev

Changed marginalize function according to new representation
used String IO in tests, included docstrings
Merge pull request #169 from ankurankan/dev

Changes in Factor class according to the new representation
Merge pull request #170 from ankurankan/dev

Noisy-Or Models
Merge pull request #163 from jp111/pomdpX

PomdpX Reader Class
Merge pull request #179 from ankurankan/dev

Factor Product and __str__ of Factor