downloading robots.txt file
get_robotstxt(domain, warn = TRUE, force = FALSE, user_agent = NULL)
domain from which to download robots.txt file
warn about being unable to download domain/robots.txt because of
if TRUE instead of using possible cached results the function will re-download the robotstxt file HTTP response status 404. If this happens,
HTTP user-agent string to be used to retrieve robots.txt file from domain