Embed original RAW

I think it would be great if the original RAW data could be (optionally) stored together inside the PureRAW DNG output. This would simplify organizing the files and allow to easily reprocess the image in the future if needed. It could be done in a DNG-compliant way e.g. by storing the original raw file in the appropriate DNG tag (for proprietary raw formats) or by storing the PureRAW output as a enhanced image inside the original file (for raw files already in the DNG format).