Add java doc with @since to indicate when it appeared

Object under question, doesn't it have some better structure?

Plus add @CheckForNull

Sounds like over naming. Class itself about stats and naming vars with stats tail under question.
@marcuslinke imho better name it as is to be closer to docker API docs. Hopefully for this variable docker devs placed normal name.

Variables are normally named like JSON fields in docker-java. But what about getter? getNetwork()/getNetworks() should return an dedicated object instead of a map, right?

I see no specific structure and wrappers for it. Until it just a map iface:stats Map looks good. But i don't like <Object> how it expected for usage?

Or do you want create the same analogue as PortBindings?

Sounds like design question. Up to @marcuslinke

Then @marcuslinke should create 2.x or 2.1 branch

There are API breaking changes already in master, so this will not work. We should really consider another branching model...

@marcuslinke just create new branch based on previous to cc5b11a (hope it has no bad changes before) then @bonigarcia will PR to this branch and you will do 2.1.3 in parallel.

OK. Done. Created branch 2.x

PR to branch 2.x in #362