help: add flags to output and ssh categories

- Add --output, --remove-on-error, --output-dir and --created-dirs to
the output help category

- Add --hostpubmd5, --hostpubsha256

help: add flags to output and ssh categories

- Add --output, --remove-on-error, --output-dir and --created-dirs to
the output help category

- Add --hostpubmd5, --hostpubsha256, --insecure (-k), and --pubkey to
the ssh help category

Closes #14076

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cmdline-opts: shorter help texts

In an effort to increase the readability of the "--help all" output on
narrow (80 column) terminals.

Co-authored-by: Jay Satiro

Closes

cmdline-opts: shorter help texts

In an effort to increase the readability of the "--help all" output on
narrow (80 column) terminals.

Co-authored-by: Jay Satiro

Closes #13169

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docs/cmdline: change to .md for cmdline docs

- switch all invidual files documenting command line options into .md,
as the documentation is now markdown-looking.

- made the

docs/cmdline: change to .md for cmdline docs

- switch all invidual files documenting command line options into .md,
as the documentation is now markdown-looking.

- made the parser treat 4-space indents as quotes

- switch to building the curl.1 manpage using the "mainpage.idx" file,
which lists the files to include to generate it, instead of using the
previous page-footer/headers. Also, those files are now also .md
ones, using the same format. I gave them underscore prefixes to make
them sort separately:
_NAME.md, _SYNOPSIS.md, _DESCRIPTION.md, _URL.md, _GLOBBING.md,
_VARIABLES.md, _OUTPUT.md, _PROTOCOLS.md, _PROGRESS.md, _VERSION.md,
_OPTIONS.md, _FILES.md, _ENVIRONMENT.md, _PROXYPREFIX.md,
_EXITCODES.md, _BUGS.md, _AUTHORS.md, _WWW.md, _SEEALSO.md

- updated test cases accordingly

Closes #12751

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