Minor updates, improvements, and bug fixes.

- Allowed status_message function to be called by others. This is to
centralize all feedback into protocol.c.

- Fixed a bug where line number words 'N' were causing the parser to
error out.

- Allowed homing routine feed rates to move slower than the
MINIMUM_STEP_RATE parameter in config.h.

- Homing performs idle lock at the end of the routine.

- Stepper idle lock time will now not disable the steppers when the
value is set at 255. This is accomodate users who prefer to keep their
axes enabled at all times.

- Moved some defines around to where they need to be.

planner.c

@@ -419,6 +419,12 @@ void plan_buffer_line(float x, float y, float z, float feed_rate, uint8_t invert
   // path width or max_jerk in the previous grbl version. This approach does not actually deviate 
   // from path, but used as a robust way to compute cornering speeds, as it takes into account the
   // nonlinearities of both the junction angle and junction velocity.
+  // NOTE: This is basically an exact path mode (G61), but it doesn't come to a complete stop unless
+  // the junction deviation value is high. In the future, if continuous mode (G64) is desired, the
+  // math here is exactly the same. Instead of motioning all the way to junction point, the machine
+  // will just need to follow the arc circle defined above and check if the arc radii are no longer
+  // than half of either line segment to ensure no overlapping. Right now, the Arduino likely doesn't
+  // have the horsepower to do these calculations at high feed rates.
   float vmax_junction = MINIMUM_PLANNER_SPEED; // Set default max junction speed
 
   // Skip first block or when previous_nominal_speed is used as a flag for homing and offset cycles.