Websocket support

[pjotterplotter]

Nice library! I was wondering if there are any plans to also support websockets (which is a nice extra fastapi provides), like these libraries do?:

https://jsonrpcclient.readthedocs.io/en/latest/
https://github.com/codemation/easyrpc

[spumer]

I think I will work with websockets in 2021 and may be implement this feature for fastapi-jsonrpc, cause it's main lib in production