Allow kwargs to be passed through to uplaoder

Rather than keep concurrent_create_archive_from_file and ConcurrentUploader in
sync with their arguments,
**kwargs is now forwarded to ConcurrentUploader so that whatever args
ConcurrentUploader may grow, concurrent_create_archive_from_file will support
those args.

I also plan on adding a few kwargs to ConcurrentUploader in the
relatively near future.