TLS: TLSv1.3 earlydata support for curl

Based on #14135, implement TLSv1.3 earlydata support for the curl
command line, libcurl and its implementation in GnuTLS.

If a known TLS

TLS: TLSv1.3 earlydata support for curl

Based on #14135, implement TLSv1.3 earlydata support for the curl
command line, libcurl and its implementation in GnuTLS.

If a known TLS session announces early data support, and the feature is
enabled *and* it is not a "connect-only" transfer, delay the TLS
handshake until the first request is being sent.

- Add --tls-earldata as new boolean command line option for curl.
- Add CURLSSLOPT_EARLYDATA to libcurl to enable use of the feature.
- Add CURLINFO_EARLYDATA_SENT_T to libcurl, reporting the amount of
bytes sent and accepted/rejected by the server.

Implementation details:
- store the ALPN protocol selected at the SSL session.
- When reusing the session and enabling earlydata, use exactly
that ALPN protocol for negoptiation with the server. When the
sessions ALPN does not match the connections ALPN, earlydata
will not be enabled.
- Check that the server selected the correct ALPN protocol for
an earlydata connect. If the server does not confirm or reports
something different, the connect fails.
- HTTP/2: delay sending the initial SETTINGS frames during connect,
if not connect-only.

Verification:
- add test_02_32 to verify earlydata GET with nghttpx.
- add test_07_70 to verify earlydata PUT with nghttpx.
- add support in 'hx-download', 'hx-upload' clients for the feature

Assisted-by: ad-chaos on github
Closes #15211

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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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docs/libcurl: generate PROTOCOLS from meta-data

Remove the PROTOCOLS section from the source files completely and
instead generate them based on the header data in the curldown files.

docs/libcurl: generate PROTOCOLS from meta-data

Remove the PROTOCOLS section from the source files completely and
instead generate them based on the header data in the curldown files.

It also generates TLS backend information for options marked for TLS as
protocol.

Closes #13175

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docs/libcurl: add TLS backend info for all TLS options

All man pages that are listed to be for TLS now must also specify
exactly what TLS backends the option works for, or use All if the

docs/libcurl: add TLS backend info for all TLS options

All man pages that are listed to be for TLS now must also specify
exactly what TLS backends the option works for, or use All if they all
work.

cd2nroff makes sure this is done and that the listed backends exist.

Closes #13168

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docs: make each libcurl man specify protocol(s)

The mandatory header now has a mandatory list of protocols for which the
manpage is relevant.

Most man pages already has a "PROTO

docs: make each libcurl man specify protocol(s)

The mandatory header now has a mandatory list of protocols for which the
manpage is relevant.

Most man pages already has a "PROTOCOLS" section, but this introduces a
stricter way to specify the relevant protocols.

cd2nroff verifies that at least one protocol is mentioned (which can be
`*`).

This information is not used just yet, but A) the PROTOCOLS section can
now instead get generated and get a unified wording across all manpages
and B) this allows us to more reliably filter/search for protocol
specific manpages/options.

Closes #13166

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curldown: Fix email address in Copyright

The curldown conversion accidentally replaced daniel@haxx.se with
just daniel.se. This reverts back to the proper email address in
the curld

curldown: Fix email address in Copyright

The curldown conversion accidentally replaced daniel@haxx.se with
just daniel.se. This reverts back to the proper email address in
the curldown docs as well as in a few other stray places where it
was incorrect (while unrelated to curldown).

Reviewed-by: Daniel Stenberg <daniel@haxx.se>
Closes: #12997

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docs: introduce "curldown" for libcurl man page format

curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of

docs: introduce "curldown" for libcurl man page format

curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of leading headers with meta-data
- Supports a small subset of markdown
- Uses .md file extensions for editors/IDE/GitHub to treat them nicely
- Generates man pages very similar to the previous ones
- Generates man pages that still convert nicely to HTML on the website
- Detects and highlights mentions of curl symbols automatically (when
their man page section is specified)

tools:

- cd2nroff: converts from curldown to nroff man page
- nroff2cd: convert an (old) nroff man page to curldown
- cdall: convert many nroff pages to curldown versions
- cd2cd: verifies and updates a curldown to latest curldown

This setup generates .3 versions of all the curldown versions at build time.

CI:

Since the documentation is now technically markdown in the eyes of many
things, the CI runs many more tests and checks on this documentation,
including proselint, link checkers and tests that make sure we capitalize the
first letter after a period...

Closes #12730

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