Change code to work with 20x4 LCD instead of 16x2

[david_2018]

@Whandall

I think 8 is alias for the custom char 0, which would be hard to keep inside a cstring,
so it would be logical to be used in createChar also.

Likely correct, 8 through 15 can be used instead of 0 through 7 to address the same custom character storage on the LCD controller.