Limit the number of rows per block and per split

We use Parquet to store raw metrics data and then query this data with Hadoop-Pig.

The issue is that sometimes we end up with small Parquet files (~80mo) that contain more than 300 000 000 rows, usually because of a constant metric which results in a very good compression. Too good. As a result we have a very few number of maps that process up to 10x more rows than the other maps and we lose the benefits of the parallelization.

The fix for that has two components I believe:
1. Be able to limit the number of rows per Parquet block (in addition to the size limit).
2. Be able to limit the number of rows per split.

**Reporter**: [Quentin Francois](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=QuentinFra)
#### Externally tracked issue: [https://github.com/apache/parquet-mr/pull/251](https://github.com/apache/parquet-mr/pull/251)

_{**Note**: *This issue was originally created as [PARQUET-344](https://issues.apache.org/jira/browse/PARQUET-344). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

まず、この issue における Parquet の行/ブロックおよび split の要件と、外部で追跡されている pull request 251 を確認し、Hadoop-Pig クエリの並列化に注意を払ってください。ブロックと split の両方で設定可能な行数制限をサポートしつつ、既存のサイズ制限の動作を維持できれば完了です。

索引モデルが issue の本文から書いたものです。