Development Mode

Different site for release vs development!

• _pkgdown.yml mode: field = release, development, auto (& unreleased)
• release (default) = single site w/ everything
  • Fine for most packages
  • readr.tidyverse.org = release (CRAN)
• devel = separate site in docs/dev
  • readr.tidyverse.org/dev = devel (pak::pak("tidyverse/readr"))
• auto = automatically switch based on vnum
• FYI unreleased basically puts devel in docs