Regex quick reference added from http://rubular.com/

Hi, I have added a table of Regex quick reference which I though might be useful to the user (personally would like to have this for easy reference). 

This is an exact copy from http://rubular.com/, because I though its no point writing it all over. But how ever I have given the reference link to http://rubular.com/ at the end of the table. 

let me know your comments and keep up the good work

cheers