A slew of advertising forecasts for the next few years were released this week, and all of them basically say the same thing, writes Bill Cromwell. Next year ad spending will be solid. Digital will get a bigger chunk of spending. Print is in a deep hurt. But there was one prediction from eMarketer that really stood out, which speaks to just how much the digital world is changing: By 2018, 26% of all U.S. ad spending will go to mobile, up from 10% of all spending this year.