flow-0.4.1

• 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