`roxygen2` requests

[dgkf]

Just keeping a few notes on changes that would help support this package in roxygen2:

• Duplicate @examples are joined with extra empty lines. Especially when testex tags are functionally special @examples tags, this introduces a lot of unintentional whitespace.
• @examplesIf changes the output value of the code, meaning that .Last.value is not what might be otherwise expected by tests.

  withAutoprint(1 + 2)
  .Last.value
  # == list(value = 3, visible = TRUE)
  

  instead would be preferred if the code that executes a @examplesIf statement returns only the value:

  if (<condition>) (if (getRversion() >= "3.4") (function(x) \{ x <- as.list(substitute(x))[-1]; invisible(withAutoprint(x, evaluated = TRUE)$value) \}) else force)(\{ # examplesIf}
  1 + 2
  \dontshow{\}) # examplesIf}