Split file each 4GB for BigQuery Quota Policy

BigQuery has following [Quota Policy](https://cloud.google.com/bigquery/quota-policy).

So, It's better to split output file each 4GB.

| File Type | Compressed | Uncompressed |
| --- | --- | --- |
| CSV | 4 GB | With new-lines in strings: 4 GB
Without new-lines in strings: 5 TB |
| JSON | 4 GB | 5TB |
## Problems
- Have to split newline(CRLF/LF/CR) at EOL, not only filesize.
- Split before output beforehand is better way than split output file, Because Embulk run multiple tasks with multiple CPU cores.