0.21.0

Release notes:

• new HID event # function count (press BOOTSEL > 2 sec). See Issue #53
• frequencies adjusted for Pico1 or Pico2 to maximise compatibility
• GFX Library updated to 1.5.3
• Raspberry Pi RP2040 Board updated to 4.4.2

RESET is still executed with BOOTSEL pressed for less than 2 sec.