Implement Custom Log Format for Synchronet webserver

It seems like there's been a few log requests recently. Rather than turning certain things on and off, it might be better just to have a common log file format configuration for the webserver. This could be defined in sbbs.ini easily enough.

https://httpd.apache.org/docs/current/mod/mod_log_config.html

This would allow each sysop to customize their log file without having to have various options in scfg.