## Motivation Add A3C implementation as presented [here](https://arxiv.org/abs/1602.01783) so that the experiments of [Rainbow](https://arxiv.org/pdf/1710.02298.pdf) can be added to the examples in further contributions. ## Solution Add A3C code like [A2C](torchrl/objectives/a2c.py) and add its paper reproduction as an example. ## Checklist - [x] I have checked that there is no similar issue in the repo (**required**)
