Combine arguments with the same description to one \item

[MichaelChirico]

This makes the set of \\item values the same between master and #61. Next will be to put those arguments in the same order too.

Code for analyzing the \arguments{\item} entries:

library(tools)

args_on_branch = function(branch) {
  system(paste('git checkout', branch))
  rd = Sys.glob("man/*.Rd")
  args = lapply(rd, function(f) {
    arguments = Filter(\(x) attr(x, "Rd_tag") == "\\arguments", parse_Rd(f))
    if (!length(arguments)) return(NULL)
    sapply(Filter(\(x) attr(x, "Rd_tag") == "\\item", arguments[[1L]]), \(x) unlist(x[[1]]))
  })
  names(args) = rd
  args
}

old = args_on_branch('master')
new = args_on_branch('roxygen')