Clarify how to handle web socket back pressure

[domoritz]

The docs should be clearer about how to handle back pressure. Right now, the explanation is

def ws_message(ws, message, opcode):
    #Ok is false if backpressure was built up, wait for drain
    ok = ws.send(message, opcode)

But how should I wait for drain? Should I busy wait before returning from the call or wait in the next call or something else?

[cirospaciari]

You should queue this in some way and use the ws_drain handler to try send it again