PARQUET-108: Parquet Memory Management in Java

PARQUET-108: Parquet Memory Management in Java.
When Parquet tries to write very large "row groups", it may causes tasks to run out of memory during dynamic partitions when a reducer may have many Parquet files open at a given time.

This patch implements a memory manager to control the total memory size used by writers and balance their memory usage, which ensures that we don't run out of memory due to writing too many row groups within a single JVM.
this should not be hard coded.
I'm not familiar with how Hive manages its memory but the Hive-parquet integration should make sure to hook into it. if more than one library assumes 50% of memory is fine it will not work.