Download captcha from a URL
download_captcha_(url, path, secure, ext, timeout)URL from which to download captcha or the name of a known source
("tjrs", "tjmg", "tjrj", "trt" or "rfb")
Folder where to save downloaded captcha
Whether or not to use ssl_verifypeer = TRUE (see
httr::GET())
Default image extension if not able to extract it automatically
Timeout for captcha download (passed on to httr::timeout())