Check whether two numeric vectors are close_enough()

[kelly-sovacool]

Really just a shortcut to all(dplyr::near(x, y, tol=10^-3) for less precision.
I like to use it in a manuscript paired with assertthat::assert_that() to make sure the numbers I report don't change drastically when I re-run code.

I also did a bit of reorganizing; moved is_nearly_whole() to R/utils.R.

Change(s) made

• Create function close_enough() to check whether two numeric vectors are fairly close.

Checklist

(Strikethrough any points that are not applicable.)

• Write unit tests for any new functionality.
• Update roxygen comments & vignettes if there are any API changes.
• Update NEWS.md if this includes any user-facing changes.
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