Pyaaf2

- Implemented red black trees in cfb!
- Fix cfb issue with fat being on sector 1

- AMA linking improvements (thanks to iluvcapra and NKnuelle)
- added python 3.7 testing
- fixed rational encoding bugs
- MXF decoding improvements

- fixed mini stream size calculation bug
- added component_at_time
- added truncate to Streams
- added support for deleting properties
- further read/write performance improvements
- fixed AFFRational float conversion bug
- added Transition test
- add_keyframe method added to VaryingValues
- introduced AUID class to deal with UUID performance issues

- read performance improvements
- pro tools wave ama support
- walk() method added for otio