Soft limit error bug fix.

- Soft limit errors were stuck in a feed hold without notifying the
user why it was in a hold. When resumed, the soft limit error would
kick in. Issue should be fixed to behave as intended. To automatically
hold and issue a soft limit alarm once the machine has come to a stop.

grbl/system.h

@@ -96,6 +96,7 @@ typedef struct {
   uint8_t abort;                 // System abort flag. Forces exit back to main loop for reset.
   uint8_t state;                 // Tracks the current state of Grbl.
   uint8_t suspend;               // System suspend bitflag variable that manages holds, cancels, and safety door.
+  uint8_t soft_limit;            // Tracks soft limit errors for the state machine (Boolean)
   uint8_t step_control;
 
   int32_t position[N_AXIS];      // Real-time machine (aka home) position vector in steps.