Reported by the new script 'scripts/copyright.pl'. The script has a
regex whitelist for the files that don't need copyright headers.
Removed three (mostly usesless) README files from docs/
Closes#5141
We're mostly saying just "curl" in lower case these days so here's a big
cleanup to adapt to this reality. A few instances are left as the
project could still formally be considered called cURL.
