What changes are proposed in this pull request?

• Added patchwork-like arithmetic operators for combining ggsurvit figures: |, -, and \.

Caveats:

• I couldn't figure out how to implement the + operator.
• I didn't implement * and & because I am not really sure what they are for!
• Because there is not 100% consistency with the patchwork operators, is it even work adding these to the pkg? I think so, because it makes it much easier to place plots side by side (no need to build the figure before placing side by side).
• User can use the patchwork operators directly, but the ggsurvfit object must first be built, then wrapped in wrap_elements(). But that is pretty confusing to most users I would imagine.

If there is an GitHub issue associated with this pull request, please provide link.
closes #96

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

• Ensure all package dependencies are installed by running renv::install()
• 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.
• If a new function was added, function included in _pkgdown.yml
• If a bug was fixed, a unit test was added for the bug check
• Run pkgdown::build_site(). Check the R console for errors, and review the rendered website.
• 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.
• R CMD Check runs without errors, warnings, and notes
• usethis::use_spell_check() runs with no spelling errors in documentation

When the branch is ready to be merged into master:

• 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).
• Increment the version number using usethis::use_version(which = "dev")
• Run codemetar::write_codemeta()
• Run usethis::use_spell_check() again
• Approve Pull Request
• Merge the PR. Please use "Squash and merge".