Added changes left out in last commit.
Added changes left out in last commit.

Users can now provide a callback to retrieve real-time statistics on
the progress of zipping files.

ZipArchive/ZipArchive,ChronicStim/ssziparchive,ChronicStim/ssziparchive,ZipArchive/ZipArchive,ChronicStim/ssziparchive,ChronicStim/ssziparchive,stephanheilner/ZipArchive,stephanheilner/ZipArchive,soffes/ssziparchive,soffes/ssziparchive,hearther/ZipArchive,ZipArchive/ZipArchive,hearther/ZipArchive,soffes/ssziparchive,hearther/ZipArchive,hearther/ZipArchive