Peanut butter has a day. So do donuts. So why shouldn't 2013's most-hyped technology also get one? General Electric is on it, folks. It has designated Dec. 3 (D3, geddit?) as the official 3D Printing Day, and has also launched a new campaign that hopes to gives elves a rest for the holidays, by 3D printing gifts instead.Here's how it works: On Dec. 3, people can pick a prototype and tweet their wish, along with the hashtag #3DPrintMyGift. The prototypes themselves are designed by celebrities including weatherman Al Roker, host Stacy London, Red Sox pitcher Craig Breslow, as well as companie...