Keymap tweaks

- Brought back Mouse Z for temporary mouse usage
- Combined Mouse and Function Keys into one Layer
- Cleaned up unused code (e.g. combos, key overrides)
- Updated all keyboards with new layer
- Updated documentation
- I think this will be it for now. Making a list somewhere else
for future enhancements

keyboards/crkbd/keymaps/t4corun/keymap.c

@@ -40,6 +40,7 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
   [_NAVIGATION] = CRKBD(LAYER_NAVIGATION),
   [_NUMBER]     = CRKBD(LAYER_NUMBER),
   [_SYMBOL]     = CRKBD(LAYER_SYMBOL),
+  [_MOUSE_FUNC] = CRKBD(LAYER_MOUSE_FUNC),
   [_CONFIG]     = CRKBD(LAYER_CONFIG)
 
 };