Use roxygen2-like style for simple links

[MichaelChirico]

Another hack at the edifice of #61: trying to migrate to roxygen2-style links first.

This PR only look for cases using style \code{\link{FUN}} on master that are winding up as \code{\link[=FUN]{FUN()}} in {roxygen2} style.

Repro code:

# Find objects linked like `\link[=FUN]{FUN()}` on roxygen branch
rd = Sys.glob("man/*.Rd")
simple_call_links = sort(unique(unlist(lapply(rd, function(f) {
  l = readLines(f)
  re = R"([\\]link\[=(.*)\]\{\1\(\)\})"
  l = grep(re, l, value=TRUE, perl=TRUE)
  idx = gregexpr(re, l, perl=TRUE)
  mapply(
    \(line, start, len) substr(line, start, start+len-1),
    l, lapply(idx, attr, "capture.start"), lapply(idx, attr, "capture.length"),
    USE.NAMES=FALSE
  )
}))))

simple_call_links = setdiff(simple_call_links, "integer64") # ambiguity of the data type vs. the function

# change to patch branch
system('git checkout roxy-links')

re = sprintf(R"([\]code\{[\]link\{(%s)\}\})", paste(gsub(".", "[.]", simple_call_links, fixed = TRUE), collapse="|"))
for (f in rd) {
  l = readLines(f)
  l = gsub(re, R"(\code{\link[=\1]{\1()}})", l)
  writeLines(l, f)
}