Adds tarball streaming

I think I've about given up on trying to improve the performance of on-the-fly zip streaming. This branch does add .tar (uncompressed tar file) and .tgz (gzip compressed tar file) download options as well, if those are of interest. The uncompressed option actually does begin streaming much more quickly but at the cost of no compression; the compressed tarball unfortunately offers no significant improvement to download performance.

I can't say whether more could be done to improve the zip streaming -- given my level of knowledge it would be trial and error testing.