Added a "sketch-trailer.h" header file

This file is meant to be included in sketch files in order to make
data available to Kaleidoscope functions. In particular, the size of
the keymaps[] array (i.e. the number of defined layers), which is
needed in order to prevent reading uninitialized memory past the end
of that array due to Key_KeymapNext_Momentary.

examples/AppSwitcher/AppSwitcher.ino

@@ -46,11 +46,6 @@ const Key keymaps[][ROWS][COLS] PROGMEM = {
 };
 /* *INDENT-ON* */
 
-// Calculate the number of layers defined in the "keymaps[]" array
-// above for use elsewhere in Kaleidoscope. Don't remove or modify
-// this line; it's used to prevent reading past the end of the array!
-const uint8_t LayerCount PROGMEM = sizeof(keymaps) / sizeof(*keymaps);
-
 
 const macro_t *macroAction(uint8_t macroIndex, uint8_t keyState) {
   switch (macroIndex) {
@@ -71,3 +66,6 @@ void setup() {
 void loop() {
   Kaleidoscope.loop();
 }
+
+// This line should always be at the end of the sketch file
+#include <sketch-trailer.h>

examples/Kaleidoscope/Kaleidoscope.ino

@@ -65,11 +65,6 @@ const Key keymaps[][ROWS][COLS] PROGMEM = {
 
 };
 
-// Calculate the number of layers defined in the "keymaps[]" array
-// above for use elsewhere in Kaleidoscope. Don't remove or modify
-// this line; it's used to prevent reading past the end of the array!
-const uint8_t LayerCount PROGMEM = sizeof(keymaps) / sizeof(*keymaps);
-
 static kaleidoscope::LEDSolidColor solidRed(60, 0, 0);
 static kaleidoscope::LEDSolidColor solidOrange(60, 20, 0);
 static kaleidoscope::LEDSolidColor solidYellow(40, 35, 0);
@@ -109,3 +104,6 @@ void setup() {
 void loop() {
   Kaleidoscope.loop();
 }
+
+// This line should always be at the end of the sketch file
+#include <sketch-trailer.h>

src/sketch-trailer.h

@@ -0,0 +1,6 @@
+#pragma once
+
+// Calculate the number of layers defined in the "keymaps[]"
+// array. This needs to be included in the sketch after "keymaps" is
+// defined
+const uint8_t LayerCount PROGMEM = sizeof(keymaps) / sizeof(*keymaps);