PARQUET-104: Fix writing empty row group at the end of the file

At then end of a parquet file, it may writes an empty rowgroup.
This happens when: numberOfRecords mod sizeOfRowGroup = 0

Author: Tianshuo Deng <tdeng@twitter.com>

Closes #66 from tsdeng/fix_empty_row_group and squashes the following commits:

10b93fb [Tianshuo Deng] rename
e3a5896 [Tianshuo Deng] format
91fa0d4 [Tianshuo Deng] fix empty row group