WebSocket is a bit weird:
1. It starts like an HTTP connection, but they send special headers.
2. We reply with special headers, one of which involves SHA1 of one of theirs.
3. We are then in WebSocket mode, where each frame starts with a 2-20 byte
header.
We relay data in a simplistic way: if either side sends something, we
read it and relay it synchronously. That avoids any gratuitous
buffering.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
