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.*}

まず、issue にリンクされている parquet-manual の例を確認し、現在の parquet-java の構成と比較します。教育用モジュールまたは例をどこに配置すべきかを特定し、Thrift、Avro、Protocol Buffers を使わずにカスタムオブジェクトを書き込み、読み取る方法を明確に示せた時点で issue は完了とします。

索引モデルが issue の本文から書いたものです。