GLOBAL MARKETS-BoJ bond buying pressures yen; U.S. stocks rise

* Yen touches multi-year lows vs dollar and euro * Nikkei index soars to highest since August 2008 * Asia, European and U.S. stocks improve NEW YORK, April 8 (Reuters) - The yen dropped for a third straight day against the dollar and the euro on Monday as the Bank of Japan began aggressive monetary easing in an attempt to beat persistent deflation, boosting stocks in most markets, though U.S. gains were limited ahead of quarterly earnings reports. The dollar rallied against