In breathless U.S. election, Twitter generates buzz not cash

By Jessica Toonkel and Amanda Becker NEW YORK/WASHINGTON (Reuters) - This year's presidential election might be the perfect microcosm of Twitter's woes.        While some of the most memorable moments of the campaign for the White House have played out on the platform, Twitter has been unable to turn the attention and activity into ad dollars or user growth.     Well suited to quick updates on a noisy and unpredictable campaign, Twitter has