Allow listening on a socket file instead of a TCP socket

Instead of listening on localhost:[some port] it'd nice to be able to listen on a socket file (e.g. /var/lib/comentario/comentario.sock), since that can make managing the connection between the fronting webserver and the application server a bit easier as you don't need to worry about keeping track of TCP port numbers.

In go I believe this is typically implemented by constructing the server with net.Listen("unix", "/var/lib/comentario/comentario.sock") or the like, and then on the fronting server it would be configured as something like:

location / {
        proxy_pass http://unix:/var/lib/comentario/comentario.sock:/;
}

in nginx, or

    ProxyPass / unix:/var/lib/comentario/comentario.sock|http://localhost/

in Apache.