Support WebSockets for control

[magik6k]

This should be easy once #24 is done, and would be really useful for things like peer-base/peer-pad#285.

[jimpick]

I've implemented this as a proof-of-concept - I borrowed the main websockets implementation from go-ws-transport and it works from WebAssembly as well. I'm using it so that I can use talk to Lotus miners (running only TCP) from a web browser via a p2pd gateway. It's a bit ugly right now ... I probably wouldn't merge this implementation, but it works.

Here's the top level project:

https://github.com/filecoin-shipyard/lotus-wasm-experiments