Don't inherit docs from readr

[jennybc]

This task was started but not finished in #461. There are still several instances of #' @inheritParams readr::some_function. Something I am currently puzzling over is why readr's namespace gets loaded during R CMD check for vroom (not a huge deal, but still seems incorrect, and can lead to test failure in certain contexts) and it appears to be happening when updating vroom's docs. Part of the ongoing task of rationalizing the relationship between readr and vroom.