Allow users to switch between color and linetype aesthetics

[ddsjoberg]

What changes are proposed in this pull request?

• By default, a model plot created with ggsurvfit() or ggcuminc() uses the color aesthetic to plot curves by the stratifying variable(s), and further, ggcuminc() uses the linetype aesthetic for plots that contain multiple outcomes (i.e. competing events). We not introduce the global option "ggsurvfit.switch-color-linetype" to switch these defaults, giving users more flexibility over the output figures. (#166)

If there is an GitHub issue associated with this pull request, please provide link. closes #166

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Reviewer Checklist (if item does not apply, mark as complete)

• [x] Ensure all package dependencies are installed by running renv::install()
• [x] PR branch has pulled the most recent updates from master branch. Ensure the pull request branch and your local version match and both have the latest updates from the master branch.
• [x] If a new function was added, function included in _pkgdown.yml
• [x] If a bug was fixed, a unit test was added for the bug check
• [x] Run pkgdown::build_site(). Check the R console for errors, and review the rendered website.
• [x] Overall code coverage remains >99.5%. Review coverage with withr::with_envvar(new = c("NOT_CRAN" = "true"), covr::report()). Begin in a fresh R session without any packages loaded.
• [x] R CMD Check runs without errors, warnings, and notes
• [x] usethis::use_spell_check() runs with no spelling errors in documentation

When the branch is ready to be merged into master:

• [x] Update NEWS.md with the changes from this pull request under the heading "# ggsurvfit (development version)". If there is an issue associated with the pull request, reference it in parentheses at the end update (see NEWS.md for examples).
• [x] Increment the version number using usethis::use_version(which = "dev")
• [x] Run codemetar::write_codemeta()
• [x] Run usethis::use_spell_check() again
• [x] Approve Pull Request
• [x] Merge the PR. Please use "Squash and merge".

[psoldath]

@ddsjoberg I download the pull request and the code works perfectly! Thank you for implementing the request.

[ddsjoberg]

Great! We'll merge this when @timtreis, a package co-author, has completed the review!

[ddsjoberg]

Thank you @timtreis for the thorough review!

vdiffr began failing everywhere (except locally) recently. I've since turned these off on GH Actions. I hope they begin working again. Previously, we had set to only run the vdiffr tests when the R version matched the current release of R and the check was being run on the same OS I develop on to avoid those kinds of failures on Linux.

I am sure if you looked at the differences in the failing vdiffr tests, there wouldn't be anything importantly different.