curl_version() shows the versions of libcurl, libssl and zlib and
supported protocols. curl_options() lists all options available in
the current version of libcurl. The dataset curl_symbols lists all
symbols (including options) provides more information about the symbols,
including when support was added/removed from libcurl.
# NOT RUN {# Available optionscurl_options()
# List proxy optionscurl_options("proxy")
# Symbol tablecurl_symbols("proxy")
# Curl/ssl version infocurl_version()
# }