- Add new option CURLOPT_RESOLVER_START_FUNCTION to set a callback that
will be called every time before a new resolve request is started
(ie before a host is resolved) with a pointer to backend-specific
resolver data. Currently this is only useful for ares.
- Add new option CURLOPT_RESOLVER_START_DATA to set a user pointer to
pass to the resolver start callback.
Closes https://github.com/curl/curl/pull/2311
