USBKeyboard: add key_code_raw API

Fixes #578

Author: facchinm

Diff for: libraries/USBHID/examples/KeyboardRaw/KeyboardRaw.ino

@@ -0,0 +1,20 @@
+#include "PluggableUSBHID.h"
+#include "USBKeyboard.h"
+
+USBKeyboard Keyboard;
+
+void setup() {
+  // put your setup code here, to run once:
+}
+
+// raw keycodes can be imported from here https://gist.github.com/MightyPork/6da26e382a7ad91b5496ee55fdc73db2#file-usb_hid_keys-h
+#define KEY_ESC     0x29 // Keyboard ESCAPE
+#define KEY_I       0x0c // Keyboard i and I
+
+void loop() {
+  // in vim, jump between INSERT and COMMAND mode
+  delay(1000);
+  Keyboard.key_code_raw(KEY_ESC);
+  delay(1000);
+  Keyboard.key_code_raw(KEY_I);
+}

Diff for: libraries/USBHID/src/USBKeyboard.cpp

@@ -463,6 +463,11 @@ int USBKeyboard::_putc(int c)
 }
 
 bool USBKeyboard::key_code(uint8_t key, uint8_t modifier)
+{
+    return key_code_raw(keymap[key].usage, modifier);
+}
+
+bool USBKeyboard::key_code_raw(uint8_t key, uint8_t modifier)
 {
     _mutex.lock();
 
@@ -472,7 +477,7 @@ bool USBKeyboard::key_code(uint8_t key, uint8_t modifier)
     report.data[0] = REPORT_ID_KEYBOARD;
     report.data[1] = modifier;
     report.data[2] = 0;
-    report.data[3] = keymap[key].usage;
+    report.data[3] = key;
     report.data[4] = 0;
     report.data[5] = 0;
     report.data[6] = 0;

Diff for: libraries/USBHID/src/USBKeyboard.h

@@ -154,6 +154,20 @@ class USBKeyboard: public USBHID, public ::mbed::Stream {
     */
     bool key_code(uint8_t key, uint8_t modifier = 0);
 
+    /**
+    * To send directly a keycode
+    *
+    * @code
+    * //To send ESC
+    *  keyboard.key_code_raw(0x29);
+    * @endcode
+    *
+    * @param modifier bit 0: KEY_CTRL, bit 1: KEY_SHIFT, bit 2: KEY_ALT (default: 0)
+    * @param key character to send
+    * @returns true if there is no error, false otherwise
+    */
+    bool key_code_raw(uint8_t key, uint8_t modifier = 0);
+
     /**
     * Send a character
     *