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
Fix heading
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.
Implement Handling on the TTP API object.
Implement Roles list on InformationSource API