Submit 3.1.0 to CRAN

• Review CRAN Repository Policy
• Push all changes to GitLab.
• rhub::check_for_cran() and wait for all results.
• rhub::check(platform = c("macos-highsierra-release", "macos-highsierra-release-cran"))
• Run GitLab-CI.
• Update cran-comments.
• Check NEWS.md
• Check DESCRIPTION

marked the checklist item rhub::check(platform = c("macos-highsierra-release", "macos-highsierra-release-cran")) as completed

marked the checklist item rhub::check_for_cran() and wait for all results. as completed

marked the checklist item Update cran-comments. as completed

marked the checklist item Check NEWS.md as completed

marked the checklist item Check DESCRIPTION as completed

marked the checklist item Review CRAN Repository Policy as completed

closed with commit 479f9501