Documented, improved and LAYOUT_FRENCH_BELGIAN fixed :-)

Author: ArminJo

README.md

@@ -19,7 +19,7 @@ Available as Arduino Board Manager entry "Digistump AVR Boards" using the Board
 - Included most [pull requests](https://github.com/digistump/DigistumpArduino/pulls) done after the 1.6.7 release like `recipe.output.tmp_file={build.project_name}.hex` in *platform.txt* and EEPROM library.
 - Added recipe to update booltloader by Arduino IDE.
 - Removed the non trusted post_install.bat since Arduino code states: `// Set main and bundled indexes as trusted` => all others are untrusted.
-- Extended `DigisparkKeyboard` library with 22 keyboard layouts from [Teensyduino Core Library](https://github.com/PaulStoffregen/cores/blob/master/teensy/keylayouts.h), fixed bugs and improved it.
+- Extended `DigisparkKeyboard` library with 22 keyboard layouts from [Teensyduino Core Library](https://github.com/PaulStoffregen/cores/blob/master/teensy/keylayouts.h), fixed bugs, **documented** and improved it. [Here](https://github.com/ArminJo/DigistumpArduino/blob/542aac12e56a1818af32b303c5709c655a12d98d/digistump-avr/libraries/DigisparkKeyboard/keylayouts.h#L80) it is documented how the mapping works, so now you can fix wrong mappings by your own (but please give me feedback to include the fix).
 
 # Installation
 To get all the benefits, just replace the old Digispark board URL **http://digistump.com/package_digistump_index.json** (e.g. in Arduino *File/Preferences*) by the new  **https://raw.githubusercontent.com/ArminJo/DigistumpArduino/master/package_digistump_index.json** and install the **Digistump AVR Boards** version **1.6.8**.

digistump-avr/libraries/DigisparkKeyboard/DigiKeyboard.h

@@ -147,13 +147,15 @@ class DigiKeyboardDevice: public Print {
         return modifier;
     }
 
+    /*
+     * Mask keycodes to ascii subset (+ a few F keys)
+     */
     uint8_t keycode_to_key(KEYCODE_TYPE keycode) {
-        uint8_t key = keycode & 0x3F;
-#ifdef KEY_NON_US_100
-        if (key == KEY_NON_US_100) {
-            key = 100;
+        uint8_t key = keycode;
+        // the only valid ASCII code > 63
+        if (keycode != KEY_NON_US_BS) {
+            key = key & 0x3F;
         }
-#endif
         return key;
     }