The dust is still settling at Yahoo after the company’s cofounder and board member Jerry Yang unexpectedly resigned Tuesday, leaving without a real explanation. Yang departed to “pursue other interests outside of Yahoo,” according to the letter he sent to the company’s chairman. Yang’s colleagues praised him for his visionary leadership, but the company suffered during his tenure as chief executive. He fought off Microsoft’s 2008 bid to buy Yahoo, but the search engine’s stock subsequently tumbled. The news of Yang’s exit bumped share prices 4 percent.