TODO: curl_multi_unblock

Closes #4418

docs/TODO

@@ -51,6 +51,7 @@
  2.4 Split connect and authentication process
  2.5 Edge-triggered sockets should work
  2.6 multi upkeep
+ 2.7 curl_multi_unblock
 
  3. Documentation
  3.2 Provide cmake config-file
@@ -447,6 +448,13 @@
 
  See https://github.com/curl/curl/issues/3199
 
+2.7 curl_multi_unblock
+
+ A portable way to unblock curl_multi_wait from another thread.
+
+ See https://github.com/curl/curl/issues/4418 and
+ https://github.com/curl/curl/wiki/curl_multi_unblock
+
 3. Documentation
 
 3.2 Provide cmake config-file