Enhancements to handle fixed types, multi-type unions and top-level unions.
Merge pull request #85 from m-a-hall/avroUnions

[PDI-9186] Add support for multi-type unions, fixed types and top-level unions to the AvroInput step
Merge branch 'master' of https://github.com/pentaho/big-data-plugin into mongoInOutImprovements