Want to in finding Invoice Clinton on Twitter? Neatly, as of Monday night you just need to sort in @PrezBillyJeff, which is a dignified deal with any former leader of the free world would be happy to own. And who can you blame — er, credit score — for it? Stephen Colbert.It was all part of Monday evening’s “Colbert Document,” which was once devoted fully to Colbert’s interview of former President Clinton, which had been …