Report version of libcurl in use.
libcurlVersion()A character string, with value the libcurl version in use or
  "" if none is.  If libcurl is available, has attributes
A character string naming the SSL/TLS implementation
    and version, possibly "none".  It is intended for the version
    of OpenSSL used, but not all implementations of libcurl use
    OpenSSL --- for example macOS reports "SecureTranspart", its
    wrapper for SSL/TLS.
A character string naming the libssh version,
    which may or may not be available (it is used for
    e.g.scp and sftp protocols). Where present,
    something like "libssh2/1.5.0".
A character vector of the names of supported protocols, also known as ‘schemes’ when part of a URL.
In late 2017 a libcurl installation was seen divided into two
  libraries, libcurl and libcurl-feature, and the first
  had been updated but not the second.  As the compiled function
  recording the version was in the latter, the version reported by
  libcurlVersion was misleading.
extSoftVersion for versions of other third-party
  software.
curlGetHeaders, download.file and
  url for functions which (optionally) use libcurl.
http://curl.haxx.se/docs/sslcerts.html and
  http://curl.haxx.se/docs/ssl-compared.html for more details on
  SSL versions (the current standard being known as TLS).  Normally
  libcurl used with R uses SecureTransport on macOS, OpenSSL on
  Windows and GnuTLS, NSS or OpenSSL on Unix-alikes.  (At the time of
  writing Debian-based Linuxen use GnuTLS and RedHat-based ones use NSS,
  but it has been announced that Fedora 27 will switch to OpenSSL.)
# NOT RUN {
libcurlVersion()
# }
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