Renamed passthru stream to raw stream.
Removed zlib extra compression parameters, so now all streams have the same basic parameter, which is compression level. And so got rid of mz_zip_compress and mz_zip_crypt structures.
Fixed issues using the disk splitting stream when the disk size was 0.
Changed return value of mz_file_exists to be consistent with all other functions.
Updated test harness and added empty zip test.