PARQUET-11: Reduce memory pressure when reading footers

based on https://github.com/apache/incubator-parquet-format/pull/2

Author: julien <julien@twitter.com>
Author: Dmitriy Ryaboy <dvryaboy@gmail.com>

Closes #7 from julienledem/reduce_metadata_memory and squashes the following commits:

96ff408 [julien] Merge branch 'master' into reduce_metadata_memory
1c382cc [julien] implement delegate instead
7664919 [Dmitriy Ryaboy] intern parquet metadata strings when reading them
Add license headers and enable apache-rat-plugin.

The RAT plugin checks for any files that do not have a license header
and fails the maven build. This helps ensure that all files are
correctly marked as they are added to the repository.
Adding NOTICE, DISCLAIMER, and KEYS.

NOTICE: All parquet code was contributed to The Apache Software
Foundation, so the NOTICE is the simple version.

DISCLAIMER: Recommended disclaimer with "Apache Parquet" as the project
and "The Apache Incubator" as the sponsor.

KEYS: Generic KEYS header, no keys yet.