updated README to include new callback arguments
updated README to include new callback arguments

ExtPoint/extnodeunit,hildjj/nodeunit,1602/nodeunit,BuZZ-dEE/nodeunit,robert-berg/rjberg-nodeunit,ExtPoint/extnodeunit,zuazo-forks/nodeunit,isaacs/nodeunit,sethmcl/nodeunit,caolan/nodeunit,sethmcl/nodeunit,caolan/nodeunit,hildjj/nodeunit,BuZZ-dEE/nodeunit