Ubiquitous shopping mall staple Auntie Anne’s is celebrating its 20th birthday by hosting a “Free Pretzel Day” Saturday from 10 a.m. to 4 p.m. at stores nationwide. Blow your New Year’s dieting resolution with your choice of an original or cinnamon sugar pretzel. Maybe next year they’ll give away tequila shots for their 21st anniversary. Any giveaway wouldn’t be complete without some sort of philanthropic twist. February 2 also marks the beginning of Auntie Anne’s…