v0.5.4 release candidate

[x] Create an rc branch
[x] Change the DESCRIPTION and NEWS on this branch to change the version number to the desired version for CRAN
[x] Commit and push to the RC branch.
[x] Make sure all upstream dependencies are accepted on CRAN.
[x] Remove Remotes from DESCRIPTION.
[x] Build package
[x] Do a sanity check by installing/testing the built package.
[x] Run R CMD check --as-cran pkg_version.tar.gz both locally and on win-builder. You can also use https://r-hub.github.io/rhub/.
[x] Perform revdepcheck.
[x] Submit to CRAN
[x] If there are R CMD check warnings that are unavoidable, make sure to explain them in the comments.
[x] Tag release
[x] Merge tag into master
[x] Delete RC branch
[x] Rebuild and deploy website
[x] Create GitHub release, and copy NEWS items into release notes
[x] Bump version number

rstudio / htmltools