Three PBS series and a reoccuring role on HBO’s “Curb Your Enthusiasm,” comedian Jack Gallagher returns to New England with his one-man show Letters to Declan. Drawing on his perspective of his own life in the 90’s and using his well-honed skills as a standup comic, Letters to Declan (Declan is his first son) is a warm and gently self-deprecating monologue about becoming a father in his 40s, with sidelights on other family relationships and a showbiz career. It’s a combination of autobiographical storytelling and humorous confessional.