By Scott DiSavino NEW YORK, Jan 20 (Reuters) - Last year looks like it was an unwelcome watershed for the embattled U.S. coal industry. Power companies in 2015 for the first time may have burned more natural gas than coal to generate electricity, according to analysts who attribute it to the cheapest gas prices in 16 years and a record number of coal-fired plants retired from service because of the high cost of meeting environmental regulations. Data from the U.S. Energy Information
