Read whole XMP from DNG

[gwegner]

I would be nice to be able to use the wrapper to extract a complete XMP-record from a DNG file and use the stay open feature as well.

-b -xmp -w! .xmp -ext DNG -r "" + rawname + """;

It would be even better to get this XMP data directly as ByteStream / String.

Thank you very much for considering!