Support RWKV models (100% RNN)

[BlinkDL]

RWKV Raven 7B Gradio DEMO: https://huggingface.co/spaces/BlinkDL/Raven-RWKV-7B

CPU INT4: https://github.com/saharNooby/rwkv.cpp

100% CUDA version: https://github.com/harrisonvanderbyl/rwkv-cpp-cuda

ONNX convertor: https://github.com/harrisonvanderbyl/rwkv-onnx

Github project: https://github.com/BlinkDL/ChatRWKV

Please let me know if you have any questions :)