Upkeep for rmapshaper (2023)

[ateucher]

• [ ] Align the names of R/ files and test/ files for workflow happiness. The docs for usethis::use_r() include a helpful script. usethis::rename_files() may be be useful.
• [ ] usethis::use_code_of_conduct()
• [ ] Remove any description of check environments from cran-comments.md
• [ ] Use lifecycle instead of artisanal deprecation messages, as described in Communicate lifecycle changes in your functions
• [ ] Add alt-text to pictures, plots, etc; see https://posit.co/blog/knitr-fig-alt/ for examples
• [ ] Update bundled mapshaper node library.

^{Created on 2023-04-25 with usethis::use_upkeep_issue(), using usethis v2.2.0}