Event when there's no metadata attached to an event, we'd still use the
constructor passing an empty metadata vector, resulting in an on-the-wire
representation with an empty trailing vector.
Particularly visible when just snooping events via websocat. There also
seems to be some bug with the timestamp -1 handling.
This only changes the script-layer API, but keeps the std::string host
in the C++ layer's ServerOptions. Mostly because the ixwebsocket library
takes host as std::string. Also, maybe at some point we'd want to
support something scheme-based like unix:///var/run/zeek.sock and placing
that in a string could not be totally wrong.
Add tests for IPV6, too.
