Documentation is on the way.
As for the interface of loading targets from json string, it was removed. The old interface is most useful when you use code generated target configuration, but it was not necessary for us to provide the json string decoding. We remove the interface is because you can always do the same thing (define and encode/decode json structure) in your code very simply, or use a different structure (like xml or something else) to record target information. Instead, we now provide an interface <ImageTarget.createFromParameters> that takes all necessary parameters for one target, so that you can combine your own target description with this interface to load one or more targets.