Feature: Add RAMPS CNC Controller Board

Created a new board to make using RAMPS as a CNC machine controller
easier. It maps pin 8 to the spindle and pin 9 to the controller fan.

Marlin/boards.h

 #define BOARD_RAMPS_13_EEB      34   // RAMPS 1.3 / 1.4 (Power outputs: Extruder0, Extruder1, Bed)
 #define BOARD_RAMPS_13_EFF      35   // RAMPS 1.3 / 1.4 (Power outputs: Extruder, Fan, Fan)
 #define BOARD_RAMPS_13_EEF      36   // RAMPS 1.3 / 1.4 (Power outputs: Extruder0, Extruder1, Fan)
+#define BOARD_RAMPS_13_SF       38   // RAMPS 1.3 / 1.4 (Power outputs: Spindle, Controller Fan)
 #define BOARD_FELIX2            37   // Felix 2.0+ Electronics Board (RAMPS like)
 #define BOARD_DUEMILANOVE_328P  4    // Duemilanove w/ ATMega328P pin assignments
 #define BOARD_GEN6              5    // Gen6

Marlin/pins.h

   #include "pins_SETHI.h"
 #elif MB(RAMPS_OLD)
   #include "pins_RAMPS_OLD.h"
-#elif MB(RAMPS_13_EFB) || MB(RAMPS_13_EEB) || MB(RAMPS_13_EFF) || MB(RAMPS_13_EEF)
+#elif MB(RAMPS_13_EFB) || MB(RAMPS_13_EEB) || MB(RAMPS_13_EFF) || MB(RAMPS_13_EEF) || MB(RAMPS_13_SF)
   #include "pins_RAMPS_13.h"
 #elif MB(DUEMILANOVE_328P)
   #include "pins_DUEMILANOVE_328P.h"

Marlin/pins_RAMPS_13.h

  *  RAMPS_13_EEB (Extruder, Extruder, Bed)
  *  RAMPS_13_EFF (Extruder, Fan, Fan)
  *  RAMPS_13_EEF (Extruder, Extruder, Fan)
+ *  RAMPS_13_SF  (Spindle, Controller Fan)
  *
  *  Other pins_MYBOARD.h files may override these defaults
  */
   #if MB(RAMPS_13_EFF)
     #define CONTROLLERFAN_PIN  -1 // Pin used for the fan to cool controller
   #endif
-#elif MB(RAMPS_13_EEF)
+#elif MB(RAMPS_13_EEF) || MB(RAMPS_13_SF)
   #define FAN_PIN            8
 #else
   #define FAN_PIN            4 // IO pin. Buffer needed
   #define HEATER_0_PIN       10   // EXTRUDER 1
 #endif
 
-#if MB(RAMPS_13_EFB)
+#if MB(RAMPS_13_EFB) || MB(RAMPS_13_SF)
   #define HEATER_1_PIN       -1
 #else
   #define HEATER_1_PIN       9    // EXTRUDER 2 (FAN On Sprinter)
 #define TEMP_1_PIN         15   // ANALOG NUMBERING
 #define TEMP_2_PIN         -1   // ANALOG NUMBERING
 
-#if MB(RAMPS_13_EFF) || MB(RAMPS_13_EEF)
+#if MB(RAMPS_13_EFF) || MB(RAMPS_13_EEF) || MB(RAMPS_13_SF)
   #define HEATER_BED_PIN     -1    // NO BED
 #else
   #define HEATER_BED_PIN     8    // BED