It is still there for backward compatibility reasons but it's not going to be supported any more. Instead use \Burzum\Imagine\Lib\ImageProcessor directly where needed.
Before it was possible to implement your own image processing methods inside your model / table, this is gone now. But you can simply retain your code by extending the ImageProcessor class and adding your custom methods there.
Please pay attention that the interface of the class has changed. It is now a fluid interface:
$processor = new ImageProcessor();
$processor
->open('foo.jpg')
->flip([/*...*/])
->rotate([/*...*/])
->thumbnail([/*...*/])
->save('foo-changed.jpg');If you implement your own methods make sure they'll return $this and that they'll have to use the protected _image property of the class.