First commit of port to STM32F3DISCOVERY board.

work-in-progress, it does compile and run though but hangs early on in
main() because of unimplemented features.

src/sensors_initialisation.c

@@ -100,7 +100,7 @@ retry:
                     break;
             }
             ; // fallthrough
-#ifndef OLIMEXINO
+#if !defined(OLIMEXINO) && !defined(STM32F3DISCOVERY)
         case ACC_MMA8452: // MMA8452
             if (mma8452Detect(&acc)) {
                 accHardware = ACC_MMA8452;