Decouple parquet-mr compression API from hadoop compression API

[Dong, Xin]

Hi, All,
Currently parquet-mr compression logic is using Hadoop compression API which 
makes parquet-mr compression highly coupled with Hadoop. Does community have 
any plan to decouple those two APIs? To make the things easier, maybe we can 
just using api similar to Hadoop compression APIs but belongs to parquet-mr 
namespace. And simply change current codec to implements the new parquet-mr 
API. Any thoughts?
Thanks,
Xin Dong