This is the first commit of 6 commits mentioned in #274, which features 1. Refactor of `Class Net` to support any form of MLP. 2. Enable type check in utils.network. 3. Relative change in docs/test/examples. 4. Move atari-related network to examples/atari/atari_network.py Co-authored-by: Trinkle23897 <trinkle23897@gmail.com>