Feature request: add --no-name flag

By default the gzip header saves a NULL-terminated filename and a timestamp. However, having these results in non-reproducible output for the same content. Therefore pigz, gzip and igzip all feature a --no-name flag in order to not include the filename and set the timestamp in the gzip header to 0. It would be great if crabz could have the same flag for inclusion in xopen. (https://github.com/pycompression/xopen). This library enhances python compression speed by piping through external programs and since a few releases back always creates reproducible output by default.