Split up pins to make it more manageable

Hopefully this is helpful to organization and future expansion….

Marlin/pins_GEN3_MONOLITHIC.h

@@ -0,0 +1,61 @@
+/**
+ * Gen3 Monolithic Electronics pin assignments
+ */
+
+#ifndef __AVR_ATmega644P__
+  #error Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu.
+#endif
+
+#define DEBUG_PIN 0
+
+// x axis
+#define X_STEP_PIN 15
+#define X_DIR_PIN 18
+#define X_MIN_PIN 20
+// Alex Checar #define X_STOP_PIN         20
+#define X_ENABLE_PIN 24 // actually uses Y_enable_pin
+#define X_MAX_PIN -1
+
+// y axis
+#define Y_STEP_PIN 23
+#define Y_DIR_PIN 22
+#define Y_MIN_PIN 25
+// Alex Checar #define Y_STOP_PIN         25
+#define Y_ENABLE_PIN 24 // shared with X_enable_pin
+#define Y_MAX_PIN -1
+
+// z axis
+#define Z_STEP_PIN 27
+#define Z_DIR_PIN 28
+#define Z_MIN_PIN 30
+// Alex Checar #define Z_STOP_PIN         30
+#define Z_ENABLE_PIN 29
+#define Z_MAX_PIN -1
+
+// extruder pins
+#define E0_STEP_PIN         12
+#define E0_DIR_PIN          17
+#define E0_ENABLE_PIN       3
+
+#define HEATER_0_PIN 16
+#define TEMP_0_PIN 0
+
+#define FAN_PIN -1
+
+// bed pins
+#define HEATER_BED_PIN -1
+#define TEMP_BED_PIN -1
+
+
+#define SDSS     -1
+#define SDPOWER          -1
+#define LED_PIN          -1
+
+// pin for controlling the PSU.
+#define PS_ON_PIN       14  // Alex, Do this work on the card?
+
+// Alex extras from Gen3+
+#define KILL_PIN           -1
+#define TEMP_1_PIN         -1
+#define TEMP_2_PIN         -1
+#define HEATER_2_PIN       -1