modular cross-platform jjmpeg

So well this isn't an announcement of a new release because i'm basically too lazy to package it up at the moment.

But I have created a modular jjmpeg for Java 11 and added support for cross compilation. I'm going to be playing with some videos for work so I thought it might be useful if I generate any tools for other users.

As part of it i've moved it's use of CObject over to using the previously mentioned nativez stuff. I also moved a bunch of the JNI utility functions over to nativez because they're generally useful elsewhere.

Who knows when i'll get to publishing it.