title: append files to an archive without reading/rewriting the whole archive
body: <p>I've got many files that I want to store in a single archive file. My first approach was to store the files in a gzipped tarball. The problem is, that I've to rewrite the whole archive if a single file is added.
  I could get rid of the gzip compression, but adding a file would still be expensive.</p>
  
  <p>What other archive format would you suggest that allows fast append operations?</p>