Parallel Training

1. Using a cluster to maintain the computation resource for parallel training.
2. Web UI for monitoring the cluster.
3. Support limiting the memory usage for each remote class.
4. Tutorial for the use of the cluster.

Example

1. Add the evolution strategies(ES) algorithm, using the PARL parallel module.
2. Append the A2C performance on a range of Atari games.
3. Append the IMPALA performance on a range of Atari games.

Tutorial

1. Add the official documentation deployed at the readthedocs.
2. Add a tutorial describing how to build a custom algorithm.
3. Add a tutorial describing how to use the cluster for parallel computation.