Car racing (#117)

* CarRacing-v0 new box2d environment

examples/agents/random_agent.py

@@ -40,6 +40,9 @@ if __name__ == '__main__':
             ob, reward, done, _ = env.step(action)
             if done:
                 break
+            # Note there's no env.render() here. But the environment still can open window and
+            # render if asked by env.monitor: it calls env.render('rgb_array') to record video.
+            # Video is not recorded every episode, see capped_cubic_video_schedule for details.
 
     # Dump result info to disk
     env.monitor.close()