1.17 Add support for IRIs
1.18 try next proxy if one doesn't work
1.20 SRV and URI DNS records
+ 1.21 Add return code to CURLMOPT_PUSHFUNCTION to fail the connection
1.22 CURLINFO_PAUSE_STATE
1.23 Offer API to flush the connection pool
1.24 TCP Fast Open for windows
Offer support for resolving SRV and URI DNS records for libcurl to know which
server to connect to for various protocols (including HTTP!).
+1.21 Add return code to CURLMOPT_PUSHFUNCTION to fail the connection
+
+ Allow the callback to return a value that would stop the entire operation,
+ like it can be done from most other callbacks.
+
+ See https://curl.haxx.se/mail/lib-2020-06/0099.html
+
1.22 CURLINFO_PAUSE_STATE
Return information about the transfer's current pause state, in both