ls331: Fix setpoint retrieval and implement setpoint setting

ls331.py

@@ -143,11 +143,17 @@ class LS331:
         r = self.ask(b'HTR?')
         return float(r)
 
-    def get_setpoint(self):
+    def get_setpoint(self, loop):
         """Temperature control loop setpoint."""
-        r = self.ask(b'SETP?')
+        assert loop == 1 or loop == 2
+        r = self.ask(b'SETP? %d' % loop)
         return float(r)
 
+    def set_setpoint(self, loop, value):
+        """Set temperature control loop setpoint."""
+        assert loop == 1 or loop == 2
+        self.send(b'SETP %d,%f' % (loop, value))
+
     def set_calibration_curve(self, curve, calibration):
         """Upload calibration data."""
         # CRVHDR <curve>, <name>, <serial>, <format>, <limit value>, <sign>