Creating an empty R package up to the best standards

Infrastructure: * The usethis package to create the package, an upkeep issue, and all the infrastructure that makes a solid package. * testthat for tests. * pkgdown for the website. * The fledge package to manage the changelog. Also: * r-lib/actions for GitHub Actions workflows (check-standard.yaml). * git, GitHub and the gh CLI for all things version control. * r-lib/rig to easily access multiple versions of R * Docker + RStudio server (in a rocker/verse image) for portable IDE.