Added restore settings defaults command.

- New restore setting defaults command. Only wipes ‘$$’ setting in
EEPROM and reloads them based on the defaults used when Grbl was
compiled. Used with a `$RST` command

NOTE: `$RST` is intentionally not listed in the Grbl ‘$’ help message.

grbl/grbl.h

@@ -23,7 +23,7 @@
 
 // Grbl versioning system
 #define GRBL_VERSION "0.9i"
-#define GRBL_VERSION_BUILD "20150529"
+#define GRBL_VERSION_BUILD "20150618"
 
 // Define standard libraries used by Grbl.
 #include <avr/io.h>

grbl/report.c

@@ -138,6 +138,8 @@ void report_feedback_message(uint8_t message_code)
     printPgmString(PSTR("Check Door")); break;
     case MESSAGE_PROGRAM_END:
     printPgmString(PSTR("Pgm End")); break;
+    case MESSAGE_RESTORE_DEFAULTS:
+    printPgmString(PSTR("Restoring defaults")); break;
   }
   printPgmString(PSTR("]\r\n"));
 }

grbl/report.h

@@ -69,6 +69,7 @@
 #define MESSAGE_DISABLED 5
 #define MESSAGE_SAFETY_DOOR_AJAR 6
 #define MESSAGE_PROGRAM_END 7
+#define MESSAGE_RESTORE_DEFAULTS 8
 
 // Prints system status messages.
 void report_status_message(uint8_t status_code);

grbl/settings.h

@@ -101,7 +101,7 @@ void settings_init();
 // Helper functions to clear and restore EEPROM defaults
 void settings_restore_global_settings();
 void settings_clear_parameters();
-void settings_clear_startup_line();
+void settings_clear_startup_lines();
 void settings_clear_build_info();
 
 // A helper method to set new settings from command line

grbl/system.c

@@ -200,7 +200,14 @@ uint8_t system_execute_line(char *line)
             } while (line[char_counter++] != 0);
             settings_store_build_info(line);
           }
-          break;                 
+          break; 
+        case 'R' : // Restore defaults [IDLE/ALARM]
+          if (line[++char_counter] != 'S') { return(STATUS_INVALID_STATEMENT); }
+          if (line[++char_counter] != 'T') { return(STATUS_INVALID_STATEMENT); }
+          if (line[++char_counter] != 0) { return(STATUS_INVALID_STATEMENT); }                        
+          report_feedback_message(MESSAGE_RESTORE_DEFAULTS);
+          settings_restore_global_settings();
+          break;
         case 'N' : // Startup lines. [IDLE/ALARM]
           if ( line[++char_counter] == 0 ) { // Print startup lines
             for (helper_var=0; helper_var < N_STARTUP_LINE; helper_var++) {