Providence Rag by Bruce DeSilva Forge/Tom Doherty & Associates, $25.99, 351 pages, ISBN 978-0-7653-7429-5 One of my favorite literary characters and amateur sleuths is a wise-cracking, cigar-chomping, hometown-homeboy ace investigative reporter and crime-fighting journalist by the name of Liam Mulligan.  He’s based in Providence, Rhode Island, working for a venerated, one hundred forty year old newspaper that’s barely managing to stay afloat, thanks mostly to the publisher’s deep sense