* Allow to specify trainer callbacks (train_fn, test_fn, stop_fn) in high-level API, adding the necessary abstractions and pass-on mechanisms * Add example atari_dqn_hl
* Refactored module `module` (split into submodules) * Basic support for discrete environments * Implement Atari env. factory * Implement DQN-based actor factory * Implement notion of reusing agent preprocessing network for critic * Add example atari_ppo_hl