Add curl_url_strerror() to convert CURLUcode into readable string and
facilitate easier troubleshooting in programs using URL API.
Extend CURLUcode with CURLU_LAST for iteration in unit tests.
Update man pages with a mention of new function.
Update example code and tests with new functionality where it fits.
Closes#7605
- avoid writing "set ..." or "enable/disable ..." or "specify ..."
*All* options for curl_easy_setopt() are about setting or enabling
things and most of the existing options didn't use that way of
description.
- start with lowercase letter, unless abbreviation. For consistency.
- Some additional touch-ups
Closes#7688
Since HTTPS is "the new normal", this update changes a lot of man page
examples to use https://example.com instead of the previous "http://..."
Closes#5969
