Memorial Day weekend in Boston has long been a time to get together with family and friends, and since 2013 the Boston Calling Music Festival has been synonymous with the long weekend. Metallica, The Foo Fighters, St. Vincent, Lizzo, Eminem, Travis Scott, Nine Inch Nails, and just about every other big band in the the world has played the event now held at The Harvard Athletic Complex.Martha Sheridan waves her backstage pass and talks to Boston Calling co-founder Brian Appel, who explai...