GLOBAL MARKETS-Dollar soars, stocks gain amid talk of Fed QE exit

* Fed's Williams says stimulus withdrawal could start this summer * U.S. consumer sentiment rises to highest in nearly six years * U.S. dollar index hits nearly three-year high, stocks climb * U.S. Treasuries prices fall further after sentiment data By Herbert Lash NEW YORK, May 17 (Reuters) - The dollar soared on Friday against a basket of currencies, reaching a nearly three-year peak, and global equity indexes gained as speculation mounted over whether the Federal Reserve