First up, a look at the great foreign currency shift of 2015. Plus, the children of the Rev. Martin Luther King Jr. have been criticized for overly protecting his speeches and writings but also commercializing them for profit. One result: you can watch the “I Have a Dream” speech on YouTube, with a Doritos commercial. And January is the busiest month for health clubs to sign up new members, as people resolve once and for all to get fit in the new year. But many people don’t go to the gym often enough to justify the expense. Economists have some theories about why that’s the case.