Two decades after its founding, Klarna has gone public, and its investors are finally seeing a windfall.The Swedish "buy now, pay later" company listed on the New York Stock Exchange on Wednesday. Its stock popped 30% on its debut, jumping above its $40-per-share IPO price to $52 a share. That IPO price gave Klarna a $15.1 billion valuation and netted Klarna $1.37 billion. Per Pitchbook, Klarna had raised $3.85 billion in its history before the public listing.Klarna's IPO has been a long time coming. Fou ...