optimize chunk scan; fix compressed size
Fix hive map and array inspectors with null containers

- This can happen if the data was not generated by Hive
- Also add unit tests on these
Update CHANGES.md
Merge pull request #234 from Parquet/optimize_chunk_scan

optimize chunk scan; fix compressed size
Merge pull request #239 from Parquet/hive_fix_null_maps

Fix hive map and array inspectors with null containers