Alpha2

Includes:

• Support for versioning schemas ( #10 ). As things change, developers can define upgrade functions so that future versions of OTIO can gracefully upgrade older versions of the schema.
• Nesting and functionality to fetch the range of nested items/compositions ( #16 #13 )
• Removing the unused "transform" property ( #12 )
• Python 3 support ( #19 #24 #20, @reinecke )
• Conversion to/from seconds for RationalTime ( #17, @reinecke )
• Cleanup on the setup.py ( #18 @reinecke )

Thank you!