- introduced support for a new RL library, stable-baselines: https://github.com/hill-a/stable-baselines
- removed and deprecated all rllab features
- introduced a multi-lane generic highway network with on- and off-ramps
- added a tutorial on running the bottleneck experiments
- added a tutorial for running RLlib experiments on EC2 servers
- some refactoring to features in grid network
- increased unit test coverage for renderer features