Fix R CMD Check issues

[elinw]

Currently I'm getting some issues

checking Rd \usage sections ... WARNING
  Undocumented arguments in documentation object 'print'
    ‘n_extra’

checking Rd cross-references ... WARNING
  Missing link or links in documentation object 'print.Rd':
    ‘tbl_format_setup’

  See section 'Cross-references' in the 'Writing R Extensions' manual

This is the generated line in print.rd that is causing the latter:

\item{...}{Passed on to \code{\link[=tbl_format_setup]{tbl_format_setup()}}.}

@michaelquinn32 You have a better sense of the documentation than I do, I think it's happening because we are pulling in from the tidyverse.

[michaelquinn32]

I think these are addressed in the outstanding PRs.

Let's merge those and double back to this then.

[elinw]

Okay I asked a couple of questions in them, but they look great.