Extend Unicode support in ASCIIfy()

[arni-magnusson]

Hi Ben,

The only thing more fun than drawing ASCII art is drawing UTF-8 art :)

Today, I wanted to ASCIIfy the └ character and was surprised that the ASCIIfy() function was choking on it. After a quick Heimlich maneuver, I modified a line in the code that allows it to convert a wider range of Unicode characters, including the highly useful └ character.

Reproducible example:

# Current gtools
source("https://raw.githubusercontent.com/r-gregmisc/gtools/bc5d659/R/ASCIIfy.R")
ASCIIfy("└")

# This pull request
source("https://raw.githubusercontent.com/arni-magnusson/gtools/refs/heads/master/R/ASCIIfy.R")
ASCIIfy("└")

[bbolker]

Merged, thanks. How would you write a test/example for this? I'm worried about including the└ character in example/test files because of potential encoding issues ... ??