Customisations for Arduino UNO R4 WiFi board with 12x8 display

[kevinjwalters]

I plan to add some specific features for the relatively new Arduino UNO R4 WiFi board.

1. Use the 12x8 display as a bar chart similar to how the one works on BBC micro:bit in MakeCode.

Other changes not specific to UNO R4 WiFi

1. Improve mains interference rejections by tweaking buffer size. (Also covered by #41)

[kevinjwalters]

An R4 WiFi can be seen in action in Instructables: XX and https://www.youtube.com/watch?v=R6umD3_ovNo