Macro based Scala APIs for Predicate and Projection push down

There has been some experiments with Scala macros to make Predicate and Projection APIs in Scala.
In particular by `[~neville]`:
https://github.com/nevillelyh/parquet-avro-extra/blob/master/parquet-avro-examples/src/main/scala/me/lyh/parquet/avro/examples/ExampleApp.scala
https://github.com/nevillelyh/parquet-avro-extra/commit/090f8d1d1d7d44489bb71e04465d4a12a46432c9#diff-89dca6adcdf105c6063661de43931c29R15

There have also been some discussion at Twitter.

**Reporter**: [Julien Le Dem](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=julienledem) / @julienledem

_{**Note**: *This issue was originally created as [PARQUET-218](https://issues.apache.org/jira/browse/PARQUET-218). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Inizia leggendo il file parquet-avro-extra ExampleApp.scala collegato e il commit referenziato, quindi confronta i relativi esperimenti con le macro Scala con le API correnti di parquet-java. L’issue è completa quando viene concordato e implementato un approccio definito basato su macro per il push down di Predicate e Projection.

Scritto dal modello di indicizzazione a partire dal testo della issue.