when turning timer on, resume remaining time instead of resetting it to initial value

include/timer.h

@@ -6,7 +6,7 @@ typedef void (*remaining_callback_t)(int8);
 struct : public CallbackAware<remaining_callback_t> {
 
     void operator=(int8 value) {
-        initial = remaining = value;
+        remaining = value;
     }
 
     operator int8() {
@@ -14,7 +14,7 @@ struct : public CallbackAware<remaining_callback_t> {
     }
 
     void start() {
-        remaining = initial + 1;
+        initial = remaining++;
     }
 
     void decrease() {