This exposes Broker's new WebSocket support in Zeek. To enable it,
call `Broker::listen_websocket()`. Zeek will then start listening on
port 9997 for incoming WebSocket connections.
See the Broker documentation for a description of the message format
expected over these WebSocket connections.
Older cmake versions have problems with the version number. When
installing OpenSSL on a 64 bit linux one also needs to create an
additional symlink to get cmake to use the correct library.