* update lr interface and support  training on single gpu

* yapf

* update warning message

* update warning message

* fix compatibility issue with the newest paddle

* remove logging lines
Co-authored-by: Nrobot <zenghongsheng@baidu.com>

* add maddpg example

* format with yapf

* fix coding style

* fix coding style

* unittest without import multiagent env

* update maddpg code

* update maddpg readme

* add copyright comments

* update parl.maddpg without import gym

* update NeurlIPS2018.gif to NeurlIPS2019.gif

* update readme and comments

* add maddpg example

* format with yapf

* fix coding style

* fix coding style

* unittest without import multiagent env

* update maddpg code

* update maddpg readme

* add copyright comments