added the beginning of an ex_02.py script
changed an attribute on MarkingStructureType from self.extension_type_ to self.extensiontype_. fixes #1
Merge branch 'master' of github.com:STIXProject/python-stix
fixed bugs. added content to ex_02.py
Merge branch 'master' of github.com:bworrell/python-stix
Merge pull request #5 from bworrell/master

fixed bugs. added more content to examples/ex_02.py