WHMP news has learned Northampton School Superintendent Brian Salzer is resigning.  Salzer will officially announce his resignation to the School Committee at its meeting next week.  The news comes as the city faces some tough choices when it comes to its schools.  Northampton is looking at a major budget shortfall, with a school budget deficit of between $350,000 and $400,000.  Salzer has also had to deal with the still-unresolved thorny issue of a possible later start time for Northampton High School.  There's no word yet on when Salzer's resignation will take effect.