options: API for meta-data about easy options

const struct curl_easyoption *curl_easy_option_by_name(const char *name);

 const struct curl_easyoption *curl_easy_option_by_id (CURLoption id);

 const struct curl_easyoption *
 curl_easy_option_next(const struct curl_easyoption *prev);

The purpose is to provide detailed enough information to allow for
example libcurl bindings to get option information at run-time about
what easy options that exist and what arguments they expect.

Assisted-by: Jeroen Ooms
Closes #5365

tests/data/test1119

@@ -27,5 +27,4 @@ Verify that symbols-in-versions and headers are in sync
 OK
 </stdout>
 </verify>
-
 </testcase>