update of api docstrings across coach and tutorials [WIP] (#91)

* updating the documentation website
* adding the built docs
* update of api docstrings across coach and tutorials 0-2
* added some missing api documentation
* New Sphinx based documentation

docs_raw/source/components/agents/value_optimization/qr_dqn.rst

@@ -0,0 +1,33 @@
+Quantile Regression DQN
+=======================
+
+**Actions space:** Discrete
+
+**References:** `Distributional Reinforcement Learning with Quantile Regression <https://arxiv.org/abs/1710.10044>`_
+
+Network Structure
+-----------------
+
+.. image:: /_static/img/design_imgs/qr_dqn.png
+   :align: center
+
+Algorithm Description
+---------------------
+
+Training the network
+++++++++++++++++++++
+
+1. Sample a batch of transitions from the replay buffer.
+
+2. First, the next state quantiles are predicted. These are used in order to calculate the targets for the network,
+   by following the Bellman equation.
+   Next, the current quantile locations for the current states are predicted, sorted, and used for calculating the
+   quantile midpoints targets.
+
+3. The network is trained with the quantile regression loss between the resulting quantile locations and the target
+   quantile locations. Only the targets of the actions that were actually taken are updated.
+
+4. Once in every few thousand steps, weights are copied from the online network to the target network.
+
+
+.. autoclass:: rl_coach.agents.qr_dqn_agent.QuantileRegressionDQNAlgorithmParameters