DQN
https://github.com/rlcode/reinforcement-learning
Policy Gradient
https://lilianweng.github.io/lil-log/2018/04/08/policy-gradient-algorithms.html#what-is-policy-gradient
https://www.skooldio.com
DDPG
https://github.com/MorvanZhou/Reinforcement-learning-with-tensorflow/blob/master/contents/9_Deep_Deterministic_Policy_Gradient_DDPG/DDPG_update2.py
https://lilianweng.github.io/lil-log/2018/04/08/policy-gradient-algorithms.html#dpg
https://yanpanlau.github.io/2016/10/11/Torcs-Keras.html
https://pemami4911.github.io/blog/2016/08/21/ddpg-rl.html
http://www.cs.sjsu.edu/faculty/pollett/masters/Semesters/Spring18/ujjawal/DDPG-Algorithm.pdf