v2021.2

• Fix issues from rev2021.1:
  • Add SN74LVC1T45DBV so that SK6812mini-e and SK6812
    get 5V data signal from minif4.
  • Fix schematic for pins PA2, PB9, PC15 to align with firmware for (jumped) rev2020.1 board.
• Use updated minif4 footprint.
  (i.e. without the redundant 5V/GND/3V3).
• Simplify reference designators.
  e.g. from J_r_1 to J_2, R_LED_1 to R4, etc.
• Add TP_1, TP_2 01x04 connection pins
  to breakout pins. Allows using other controller to
  test the RGB LEDs, or using the board to test other
  RGB LED strips.
• Add PCB artwork.

Kicad: update PCB for keyboard 100x100 minif4 36-key
Changelog:

• Update per the schematic:
  • e.g. fix issue from rev2021.1:
    • add LVC,
    • adjust position of top-right hole for M2 spacer.
  • add breakout pins for RGB in/out.
  • use the other 5V, 3V3, GND pins of the minif4.
• Use thinner traces for signal traces.
• Route so as to maximize the GND zone fill on back copper layer,
  try keep signal traces far apart.