Closes the server and completely exits.

To enable this function for use on your server, add -allowquit to your commandline, which will make this function run quit keep_players when executed, this also does not forcibly disconnect players.

This is also available when running in server test mode (launch option -systemtest). Server test mode is used internally at Facepunch as part of the build process to make sure that the dedicated servers aren't crashing on startup.