It would be awesome if you can supply a configurable directive like `log_format`. For example:

    req_status_zone name=server key="$host,$server_addr:$server_port" format="%C %R %I %O" size=10M;

%C means connection counter
%R means request counter
%I means bytes in counter
%O means bytes out counter
%T means mean request time counter
%2 means 2XX response counter
%3 means 3XX response counter
etc...