Version 2.0.0 Beta 1

• Add DNSQuery, DNSRecord, SocketAddress objects.
• Add 'title' and 'description' to Observables.
• Update StructuredText type with simpler structure.
• Update ExtractedString(s) and EnvironmentVariable(s) types.
• Update EmailMessage, File, Port, and Process objects.
• Extract PatternFieldGroup attributes into a separate class.
• Support lists of values within Properties.
• Support ControlledVocabularyStrings.
• Wrap content in CDATA where appropriate.
• Allow EntityList to enforce the type of objects that are added to it.
• Make XML output more readable. Don't output default attributes.
• Use proper prefixes in auto-generated IDs.
• Update helper.py.
• Improve automated tests.
• Various bugfixes, typo corrections, and style fixes.