New skill: Upgrading R dependency

[hadley]

Would be a little advice on bumping description and adding a news bullet, but would mostly consist of a brief list of todo bullets for each release, e.g. for 4.0.0:

• Switch to base pipe
• Replace purrr ~ and inline function() with \()
• Drop stringsAsFactors = FALSE
• Use raw strings for strings with many \\ escapes

(e.g. https://github.com/r-lib/roxygen2/pull/1750/changes)

Bullets for other versions could include when to drop various backports (e.g. isFALSE)