Changed the behavior of VocabString.lookup_class() to return the VocabString class when the lookup fails
Changed nsparser get_namespaces() logic to play nicer with documents that utilize non-STIX namespaces. Tests fine with the STIX sample documents, but could use some more testing.
Updated nsparser code to detect namespaces on user-defined controlled vocabuarlies. Significant changes to code that walks the python object model to retrieve namespaces and xsi_type attribute values
Initial commit of walk() and find() methods on the stix.Entity class
Merge remote-tracking branch 'origin/master' into walk
Fixed issue where ObjectProperties._parent caused duplication of yielded walk objects
Fixed bug in descend(). Changed yieldable tuple to be just stix and cybox Entity classes
Update ex_walk.py
Merge remote-tracking branch 'origin/master' into walk
Small cleanup
Merge pull request #155 from STIXProject/walk

Added walk() and find() methods
Added status to Incident. Fixes #153
Added handling to Incident class. Fixes #151
Added history to Incident class. Added stix.incident.history module with classes for History, HistoryItem, and JournalEntry
Initial commit of Yara Test Mechanism. Resolves #154
Fixed issue where improper namespace was being exported on Snort TM. Fixes #148
Fixed issue with TM extensions where incorrect namespaces were being exported on inherited fields
Added GenericTestMechanism. Resolves #143
Fix bug where stix.core.ttps was not being output.

If there are kill chain phases but no TTPs, the __nonzero__ function
on EntityList returns False, even though there is content to output.
Reduce the items that appear on documentation index page.