Provide example to write/save your own object (without thrift, avro, protoc)

I am studying parquet and found that it is not so easy to grasp the basic mechanism for writing/reading your own objects to a parquet file when you are not using protocol buffer, avro or thrift.

So my wish is to have a module that cover this topic.
I think for educational purposes it may have some value as it would help people get into the code.

I did the exercice, the code is here:
https://github.com/nromanetti/parquet-mr/tree/master/parquet-manual

**Reporter**: [Nicolas Romanetti](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=nicolasr)

_{**Note**: *This issue was originally created as [PARQUET-420](https://issues.apache.org/jira/browse/PARQUET-420). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Comienza revisando el ejemplo de parquet-manual enlazado en el issue y compáralo con la estructura actual de parquet-java. Identifica dónde encajaría un módulo educativo o un ejemplo, y considera el issue completo cuando demuestre claramente cómo escribir y leer objetos personalizados sin Thrift, Avro ni Protocol Buffers.

Escrito por el modelo de indexación a partir del texto del issue.