------------------
- tvapi.py, tvapy.rst: Fix typo in usage.
- Documentation fixes.
- Add optional test to compare threat IDs to PAN-OS exported threat
content IDs.
- Add test for release_notes(version='latest').
- tvapi.py, tvapy.rst: Allow path or '-' (stdin) for id, name, md5,
sha256 arguments.
- tvapi.py: IOError merged into OSError as of Python 3.3.
- Rework /threats/history tests to take into account retention policy.