add zlib compression to websocket

[cmdrk]

For ENet, we automatically set compression on the server side:

    % Start ENet
    Options = [
        {peer_limit, ?PEER_LIMIT},
        {channel_limit, ?CHANNEL_LIMIT},
        {compression_mode, zlib}
    ],

And on the client we correspondingly set:

    # Set mode to ZLIB
    _enet_peer.host.compress(ENetConnection.COMPRESS_ZLIB)

We need to do the equivalent thing for WebSocket if possible.