(Reuters) - rose to $70,206 at 20:03 GMT on Monday, adding $3,931 to its previous close. The world's biggest and best-known cryptocurrency is up 82.3% from the year's low of $38,505 on Jan. 23. Ether, the coin linked to the ethereum blockchain network, rose 13.3% on Monday to $3500. The approval and launch of spot bitcoin exchange-traded funds in the U.S. this year has opened the asset class to new investors and reignited the excitement that evaporated when prices collapsed in the "crypto...