The audio data is now read up to the last track's end, rather than to
the NRG footer ("first chunk offset"), unless there are no DAOX tracks.
This should be strictly equivalent in normal cases.
The audio data was initially read and written by chunks of 2352 bytes,
which is the usual sector size for audio CDs. However, this didn't work
on images with a 2448-byte sector size (2352 bytes data + 96 bytes
sub-channel data): we would end up reading data from the NRG footer.
The data is now read/written by 4 MiB (which is faster anyway), and we
make sure to read the remaining bytes if the audio data size is not a
multiple of 4 MiB.
* Use PathBuf operations to generate output file names.
* Output files are now written to the working directory.
* The cue sheet contains only the image's base name, not the full path.
Matteo Cypriani