misc: cleanup after removing years from copyright

- remove leftover copyright years from few test files
- fix email in copyright lines
- consistent format of copyright lines

misc: cleanup after removing years from copyright

- remove leftover copyright years from few test files
- fix email in copyright lines
- consistent format of copyright lines

Closes #14312

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curldown: fixups

- make DEFAULT sections less repetitive

- make historic mentions use HISTORY

- generate the protocols section on `# %PROTOCOLS%` instead of guessing

curldown: fixups

- make DEFAULT sections less repetitive

- make historic mentions use HISTORY

- generate the protocols section on `# %PROTOCOLS%` instead of guessing
where to put it

- generate the availability section on `# %AVAILABILITY%` instead of
guessing where to put it

- make the protocols section more verbose

Closes #14227

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curldown: make 'added-in:' a mandatory header field

- generate AVAILABILITY manpage sections automatically - for consistent
wording

- allows us to double-check against other d

curldown: make 'added-in:' a mandatory header field

- generate AVAILABILITY manpage sections automatically - for consistent
wording

- allows us to double-check against other documumentation (symbols-in-versions
etc)

- enables proper automation/scripting based on this data

- lots of them were wrong or missing in the manpages

- several of them repeated (sometimes mismatching) backend support info

Add test 1488 to verify "added-in" version numbers against
symbols-in-versions.

Closes #14217

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tcpkeepalive: add CURLOPT_TCP_KEEPCNT and --keepalive-cnt

Closes #13885