Closes #883

When CURLOPT_POSTFIELDS is set to an empty string libcurl will send a
zero-byte POST. Prior to this change it was documented as sending data
from the read callback.

This also changes the wording of what happens when empty or NULL so that
it's hopefully easier to understand for people whose primary language
isn't English.

Bug: https://github.com/curl/curl/issues/862
Reported-by: Askar Safin

- Remove some erroneous text.

Closes https://github.com/curl/curl/pull/865

Closes #850

Closes #822

Adds access to the effectively used http version to both libcurl and
curl.

Closes #799

Bug: https://github.com/curl/curl/issues/826
Reported-by: Michael Wallner

Now giving credit properly to github user names, fixed some UTF-8 issues
and added names discovered when contrithanks was improved.

Closes #821

The connect-to list isn't copied so as long as the handle may be used
for a transfer the list must be valid.

Bug: https://github.com/curl/curl/pull/819
Reported-by: Michael Kaufmann

Closes https://github.com/curl/curl/pull/816

Reported-by: Paul Howarth
Bug: https://curl.haxx.se/mail/lib-2016-05/0116.html

Closes #811

Closes #762

Because the old OpenSSL link now redirects to their master documentation
(currently 1.1.0), which does not document the required actions for
OpenSSL <= 1.0.2.

Closes #727

Mention possible content-length mismatch with sum of bytes reported
by write callbacks when auto decoding is enabled.

See #785

Closes #786

As discussed in #785

Reported-by: mgendre
Closes #784