textproc/py-parsimonious: Update to 0.8.0

Register devel/py-six as dependency

• Make Grammar iteration ordered, making the repr more like the original input. (Lucas Wiman)
• Improve text representation and error messages for anonymous subexpressions. (Lucas Wiman)
• Expose BadGrammar and VisitationError as top-level imports.
• No longer crash when you try to compare a Node to an instance of a different class. (Esben Sonne)
• Pin six at 1.9.0 to ensure we have python_2_unicode_compatible. (Sam Raker)
• Drop Python 2.6 support.