TODO: two possible name resolver improvements

 1.9 Cache negative name resolves

 1.10 auto-detect proxy

 1.11 minimize dependencies with dynamically loaded modules

 1.12 updated DNS server while running

 1.13 DNS-over-HTTPS

 1.14 Typesafe curl_easy_setopt()

 1.15 Monitor connections in the connection pool

 1.16 Try to URL encode given URL

 app/invoke/used protocols would be necessary to load.  See

 https://github.com/curl/curl/issues/349

1.12 updated DNS server while running

 If /etc/resolv.conf gets updated while a program using libcurl is running, it

 is may cause name resolves to fail unless res_init() is called. We should

 consider calling res_init() + retry once unconditionally on all name resolve

 failures to mitigate against this. Firefox works like that. Note that Windows

 doesn't have res_init() or an alternative.

 https://github.com/curl/curl/issues/2251

1.13 DNS-over-HTTPS

 By adding support for DNS-over-HTTPS curl could resolve host names using a

 totally separate name server than the standard system resolver, while at the

 same time doing so over a communication channel that enhances privacy and

 security.

 https://github.com/curl/curl/wiki/DNS-over-HTTPS

1.14 Typesafe curl_easy_setopt()

 One of the most common problems in libcurl using applications is the lack of