• #10 Partial fix. Improved CDATA handling in bindings and API classes.
  Added stix.utils.cdata() and stix.utils.strip_cdata() methods.
• #29 Moved duplicated binding code to stix.bindings module
• #163 Performance enhancements in to_xml() serialization
• #148 #202 #210 #214 Fixed several issues with extensions.
• #171 Indicator @negate attribute not exported unless set
• #173 Versions on core constructs are only output if set by user.
• #174 Non-core constructs no longer get auto-assigned IDs.
• #184 Added include_schemalocs parameter to to_xml() for optional
  schemalocation output
• #199 Improvements to data marking __init__ methods (thanks @benjamin9999!)
• #201 Added short_description property to stix.core.STIXHeader class
• #202 Fixed TOU marking schemalocation
• #209 Removed Python warning that is raised when trying to resolve
  schemalocation for id namespace.
• #215 Fixed typos in Incident class (thanks @DavidWatersHub!)
• Added more docs to stix.readthedocs.org