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.

protocol.h

@@ -30,6 +30,8 @@
 #define STATUS_INVALID_COMMAND 6
 #define STATUS_SETTING_DISABLED 7
 
+#define LINE_BUFFER_SIZE 50
+
 // Initialize the serial protocol
 void protocol_init();
 
@@ -43,4 +45,7 @@ uint8_t protocol_execute_line(char *line);
 // Checks and executes a runtime command at various stop points in main program
 void protocol_execute_runtime();
 
+// Prints g-code parser status message.
+void protocol_status_message(int8_t status_code);
+
 #endif