Upkeep for leaflet (2023)

[Garrick Aden-Buie]

Noticed here

• Update copyright year
• Update cph to Posit, PBC
• #867 (update copyright years)
• Check https://r-spatial.org/r/2023/05/15/evolution4.html for things we might need to do

Suggested by usethis

• usethis::use_readme_rmd()
• usethis::use_roxygen_md()
• usethis::use_github_links()
• usethis::use_pkgdown_github_pages()
• usethis::use_tidy_description()
• usethis::use_package_doc()
  Consider letting usethis manage your @importFrom directives here. usethis::use_import_from() is handy for this.
• 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 description of test environments from cran-comments.md.
  See usethis::use_cran_comments().
• Add alt-text to pictures, plots, etc; see https://posit.co/blog/knitr-fig-alt/ for examples

Set up or update GitHub Actions.
Updating workflows to the latest version will often fix troublesome actions:

• usethis::use_github_action('check-standard')
• usethis::use_github_action('test-coverage')

^{Created on 2023-08-01 with usethis::use_upkeep_issue(), using usethis v2.1.6.9000}