* remove dummy net; delete two files
* split code to have backbone and head
* rename class
* change torch.float to torch.float32
* use flatten(1) instead of view(batch, -1)
* remove dummy net in docs
* bugfix for rnn
* fix cuda error
* minor fix of docs
* do not change the example code in dqn tutorial, since it is for demonstration
Co-authored-by: Trinkle23897 <463003665@qq.com>