Update parquet spec to 2.0 and add decimal logical type.

Change-Id: I1a4cbe73a2494f8b2dd09f44bfcc0a019e710344
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2772
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: Nong Li <nong@cloudera.com>