Exec websocket

Here's some commits that use websockets to do the shell instead of direct sockets. I've left the 'shell' command for now since it still does bash a bit better than exec. When I fix those, I'll delete the shell command.

Right now there is no muxing of stdout/stderr (I didn't see how to get it out of the pty library, although I didn't look very hard). I'll look into that as well.