Upgrade to newer XMP Toolkit sdk

[crass]

Currently we're at 5.1.2, but that's like 5 or more years old. There is a much newer version "XMP Toolkit SDK CC-2016.07" from Adobe here. I've looked very briefly into upgrading but the directory structure for the files have changed and perhaps the API too. Unfortunately, there's no changelog that I can find that might give me a reason to upgrade (eg. security fixes).

So I have not compelling reason to upgrade the library right now, in particular because currently things compile well enough and I'm not really actively developing this project. gcc 6.2 spits out all kinds of warnings when compiling on Ubuntu, but it does compile. On launchpad I've had to build with -fpermissive to get it to build, though it appears to work.

I'm willing to accept a pull request if this would be something anyone wanted.