Merge pull request #90 from ankurankan/dev

Tests for Factor Class
Merge pull request #91 from ankurankan/dev

correct tests
Merge pull request #92 from ankurankan/dev

tests for factor_product
Merge pull request #94 from ankurankan/dev

correct order of public methods in docs
Merge pull request #95 from ankurankan/dev

Tests for TabularCPD
Merge pull request #96 from ankurankan/dev

TabularCPD tests
issue74 tests for is_acitve_trail and acitve_trail_nodes
Merge pull request #97 from jp111/one

issue74 tests for is_acitve_trail and acitve_trail_nodes
added XMLBIF reader
added tests for XMLBIF
corrected indentation error and added newline
class name changed
new line added in __init__.py
added get_property method for property tag alongwith tests
modified methods for strings
modified tests
modified __init__ method
added test for reading from file
replaced file open and close with 'with open'