added comments active_trail_nodes function
.idea added to .gitignore
Changed condition on _all_parents_mentioned to condition on _no_missing_parents and _no_extra_parents & same for states
Changed start_node and end_node in add_edges() to tail_node and head_node respectively. (Shikhar)
Changed get_parents to return a list instead of a generator
Changed _rule_for_parents to return list instead of generator. Added TODO to make it into a generator.
Changed _rule_for_states to return list instead of generator. Added TODO to make it into a generator.
Changed get_states() to return a list instead of  a generator. Added TODO to make it into a generator.
Changed get_parents() to return a list instead of  a generator. Added TODO to make it into a generator.
Added marginal_probability()
Changed marginal_probability function to multipy on sparse matrix
.idea file removed
Merge pull request #28 from ankurankan/dev

Remove docs
Merge pull request #29 from ankurankan/dev

Ported tests to python3
Merge pull request #30 from ankurankan/dev

updated travis.yml
Merge pull request #31 from ankurankan/dev

update travis.yml
Revert "update travis.yml"

This reverts commit cdafc22c6d88f0afb997344471fab3bfe3b84b39.
Revert "Revert "update travis.yml""

This reverts commit d0630250887fcadcf78b126a0c9a9288400ae04f.
Revert "redundant code in is_active_trail"

This reverts commit cee5ea538487b8ab0ea23567e6e8d558bbe5d718.
Merge branch 'dev' of https://github.com/pgmpy/pgmpy into dev