hid: Add example for using keyboard modifiers

libraries/USBHID/examples/KeyboardModifiers/KeyboardModifiers.ino

@@ -0,0 +1,33 @@
+/*
+  KeyboardModifiers
+
+  Select one word each second while extending the current text selection.
+
+  The purpose of this demo is to demonstrate how to use the modifier keys.
+  Some keys such as the arrow and function keys are mapped in a list so you 
+  don't have to know the key codes. You can find them in the file USBKeyboard.h.
+
+  For these keys you can use the function key_code(). 
+  For other keys such as character keys you need to look up the key codes 
+  and use the key_code_raw() function.
+
+  Author: Sebastian Romero @sebromero
+
+  This example code is in the public domain.
+*/
+
+#include "PluggableUSBHID.h"
+#include "USBKeyboard.h"
+
+USBKeyboard Keyboard;
+
+void setup() {}
+
+void loop() {  
+  delay(1000);
+  Keyboard.key_code(RIGHT_ARROW, KEY_SHIFT | KEY_ALT);
+
+  delay(1000);
+  // Alternatively you can use the raw key code for RIGHT_ARROW 0x4f
+  Keyboard.key_code_raw(0x4f, KEY_SHIFT | KEY_ALT);
+}