misc: assorted typo fixes

Closes #6375

TODO: alt-svc should fallback if alt-svc doesn't work

Closes #4908

TODO: Prevent terminal injection when writing to terminal

Closes #6150

TODO: Package curl for Windows in a signed installer

Closes #5424

docs: Fix some typos

[skip ci]

curl.se: new home

Closes #6172

TODO: Add OpenBSD libtool notice

See #5862
Closes #6030

TODO: SSH over HTTPS proxy with more backends

... as right now only the libssh2 backend supports it.

TODO: dynamically decide to use socketpair

Suggested-by: Anders Bakken

Closes #4829

TODO: add PR reference for native IDN support on macOS

As there was work started on this that never got completed.

Closes #5371

curl: add --output-dir

Works with --create-dirs and with -J

Add test 3008, 3009, 3011, 3012 and 3013 to verify.

Closes #5637

TODO: Virtual external sockets

Closes #5835

TODO: Use multiple parallel transfers for a single download

Closes #5774

TODO: Set the modification date on an uploaded file

Closes #5768

TODO: Schannel: 'Add option to allow abrupt server closure'

We should offer an option to allow abrupt server closures (server closes
SSL transfer without sending a known termination poin

TODO: Schannel: 'Add option to allow abrupt server closure'

We should offer an option to allow abrupt server closures (server closes
SSL transfer without sending a known termination point such as length of
transfer or close_notify alert). Abrupt server closures are usually
because of misconfigured or very old servers.

Closes https://github.com/curl/curl/issues/4427

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CURL_PUSH_ERROROUT: allow the push callback to fail the parent stream

... by adding support for a new dedicated return code.

Suggested-by: Jonathan Cardoso
Assisted-by: Erik Joh

CURL_PUSH_ERROROUT: allow the push callback to fail the parent stream

... by adding support for a new dedicated return code.

Suggested-by: Jonathan Cardoso
Assisted-by: Erik Johansson
URL: https://curl.haxx.se/mail/lib-2020-06/0099.html
Closes #5636

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TODO: Add flag to specify download directory

TODO: return code to CURLMOPT_PUSHFUNCTION to fail connection

TODO: retry on the redirected-to URL

Closes #5462

TODO: remove 19.3 section title

Follow-up to ad6416986755e417c66e2c6, which caused wrong formatting on
curl documentation website

Closes #5561

urldata: fix comments: Curl_done() is called multi_done() now

... since 575e885db

all: fix codespell errors

Reviewed-by: Jay Satiro
Reviewed-by: Daniel Stenberg
Closes https://github.com/curl/curl/pull/5452

TODO: --dry-run

Closes #5426

TODO: Ratelimit or wait between serial requests

Closes #5406

TODO: forbid TLS post-handshake auth and do TLS record padding

Closes #5396
Closes #5398