v0.9: Version 0.9

Changelog:
- Introduced context attributes
- Add API for querying the list of enabled backends
- IIOD can now serve over USB (using FunctionFS)
- Fix occasional buffer drops in IIOD
- Python bindings are now compatible with Python 3
- Add support for scanning in Python bindings
- Fix USB backend on Windows >= 8.1
- Add auto context creation in iio_readdev/iio_info
- Lots, lots of bug fixes