[libgdf-PR-146] Parquet reader multithread

[mike-wendt]

Evaluate to see what work from this PR can be moved to libcudf: rapidsai/libgdf#146

[harrism]

I believe @williamBlazing is adding Parquet reader to cuIO rather than cuDF. William can you comment here?

[BradReesWork]

Blazing is working on getting a Parquet PR against cuDF soon. Should this issue be closed?

[kkraus14]

Closing this as cuIO team is taking this over.