Read and write Avro data in Trevni column files.

## Limitations

The current implementation does not correctly handle all Avro data. In particular:

- Recursive types are not supported.
- With ReflectData, fields of Java type byte, short and char are not supported. Instead use int.
- With ReflectData, Java arrays are not supported. Instead use List.
- An enum is always read as a GenericData.EnumSymbol, even when SpecificData or ReflectData are used.