This week the football world ascended dizzying heights of breathlessness over the retirement of Sir Alex Ferguson. But as one footballing titan steps down, another - a man who is, in some ways, the antithesis of Sir Alex - is about to step up to take on one of the highest-profile jobs in world football. Tim Franks profiles Pep Guardiola, and asks whether he could be Sir Alex's successor as perhaps the most successful manager in the game.