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.

settings.h

@@ -29,7 +29,7 @@
 
 // Version of the EEPROM data. Will be used to migrate existing data from older versions of Grbl
 // when firmware is upgraded. Always stored in byte 0 of eeprom
-#define SETTINGS_VERSION 52
+#define SETTINGS_VERSION 53
 
 // Define bit flag masks in settings.flag.
 #define FLAG_BIT_HOMING_ENABLE      bit(0)
@@ -68,4 +68,6 @@ uint8_t settings_execute_line(char *line);
 // A helper method to set new settings from command line
 void settings_store_setting(int parameter, float value);
 
+// int8_t settings_execute_startup();
+
 #endif