Changes for version 0.104
- Fix some signedness and missing return values that resulted in incorrect error messages being reported.
- Don't overwrite existing error code if xd3_close_stream fails. This caused write errors to be mis-reported.
- Don't lseek() target/delta fds because this behaviour might be surprising
- Throw exceptions when closed or memory-mapped file handles are passed in instead of regular files.
- Vcdiff::Xdelta3 - Xdelta3 backend for Vcdiff