Curl and libcurl 7.58.0

 Public curl releases:         172
 Command line options:         211
 curl_easy_setopt() options:   249
 Public functions in libcurl:  74
 Contributors:                 1649

This release includes the following changes:

 o new libssh-powered SSH SCP/SFTP back-end
 o curl-config: add --ssl-backends [10]

This release includes the following bugfixes:

 o travis: add boringssl build [1]
 o examples/xmlstream.c: don't switch off CURL_GLOBAL_SSL [2]
 o SSL: Avoid magic allocation of SSL backend specific data [3]
 o lib: don't export all symbols, just everything curl_* [4]
 o libssh2: send the correct CURLE error code on scp file not found
 o libssh2: return CURLE_UPLOAD_FAILED on failure to upload
 o openssl: enable pkcs12 in boringssl builds [5]
 o libssh2: remove dead code from SSH_SFTP_QUOTE [6]
 o sasl_getmesssage: make sure we have a long enough string to pass [7]
 o conncache: fix several lock issues [8]
 o threaded-shared-conn.c: new example
 o conncache: only allow multiplexing within same multi handle [9]
 o configure: check for netinet/in6.h [11]
 o URL: tolerate backslash after drive letter for FILE: [12]

This release includes the following known bugs:

 o see docs/KNOWN_BUGS (https://curl.haxx.se/docs/knownbugs.html)

This release would not have looked like this without help, code, reports and
advice from friends like these:

  ahodesuka on github, Daniel Stenberg, David Benjamin, Dima Tisnek,
  guitared on github, Jan Ehrhardt, Johannes Schindelin, Matthew Kerwin,
  Nikos Mavrogiannopoulos, Oleg Pudeyev, Patrick Dawson, Randall S. Becker,
  Ray Satiro, W. Mark Kubacki,
  (14 contributors)

        Thanks! (and sorry if I forgot to mention someone)

References to bug reports and discussions on issues:

 [1] = https://curl.haxx.se/bug/?i=2118
 [2] = https://curl.haxx.se/mail/lib-2017-12/0000.html
 [3] = https://curl.haxx.se/bug/?i=2119
 [4] = https://curl.haxx.se/bug/?i=2127
 [5] = https://curl.haxx.se/bug/?i=2134
 [6] = https://curl.haxx.se/bug/?i=2143
 [7] = https://curl.haxx.se/bug/?i=2150
 [8] = https://curl.haxx.se/bug/?i=2132
 [9] = https://curl.haxx.se/bug/?i=2152
 [10] = https://curl.haxx.se/bug/?i=2128
 [11] = https://curl.haxx.se/bug/?i=2146
 [12] = https://curl.haxx.se/bug/?i=2154