Microsoft.Analytics.Samples.Formats.Avro is broken

The AvroExtractor.Extract method, `public override IEnumerable Extract(IUnstructuredReader input, IUpdatableRow output)`, uses the Length of the input stream. However, the Length property on the BaseStream is no longer supported, and when I try to run it I get this error:

> The [Length] property of [IUnstructuredReader.BaseStream] is intentionally not supported to avoid ambiguity between the physical length of [IUnstructuredReader.BaseStream] and the logical length of the split of the entire input stream assigned to a vertex.

The solution is available in this repo here: https://github.com/Azure/usql/tree/master/Examples/DataFormats