Update .gitignore and .Rbuildignore with projr-managed ignores
      projr_ignore_auto.RdThe projr_ignore_auto() function updates the project’s .gitignore and
.Rbuildignore files to reflect directories and files managed by
projr, as well as
other directories and files that should
clearly be ignored.
They are kept up-to-date with the project's configuration,
and are written within a demarcated section of the file.