... now with a -formadd suffix. While the new mime API is introduced in
7.56.0 we must acknowledge that lots of users can't upgrade their curl
versions immediately.

Include a guide to form/mime API conversion.

Closes #1922

Closes #1921

- Use spaces instead of tabs as the delimiter.

Follow up to 7c52b12d which added the entry. The entry had used tabs but
the symbol-scan parser doesn't recognize tabs and would fail the symbol.

...fixup from b8e0fe19

... it just returns error:

Bug: https://github.com/curl/curl/commit/1328f69d53f2f2e937696ea954c480412b018451#commitcomment-24470367
Reported-by: Marcel Raad

Closes #1906

Also suppress length argument of curl_mime_name() (names are always
zero-terminated).

Otherwise, typecheck-gcc.h warns on MinGW-w64.

CA path processing was implemented when mbedtls.c was added to libcurl
in fe7590f7, but it was never enabled.

Bug: https://github.com/curl/curl/issues/1877


Reported-by:  <SBKarr@users.noreply.github.com>

It has already been fixed in 6140dfcf

curl_mime_encoder() is operational and documented.
curl tool -F option is extended with ";encoder=".
curl tool --libcurl option generates calls to curl_mime_encoder().
New encoder tests 648 & 649.
Test 1404 extended with an encoder specification.

and some minor whitespace fixes

... since people copy and paste code from this example and thus they get
an inefficient POST operation without a good reason and sometimes
without understanding why.

Instead this now returns as much data as possible.

To support telling a string is nul-terminated, symbol CURL_ZERO_TERMINATED
has been introduced.

Documentation updated accordingly.

symbols in versions updated. Added form API symbols deprecation info.

This feature is badly supported in Windows: as a replacement, a caller has
to use curl_mime_data_cb() with fread, fseek and possibly fclose
callbacks to process opened files.

The cli tool and documentation are updated accordingly.

The feature is however kept internally for form API compatibility, with
the known caveats it always had.

As a side effect, stdin size is not determined by the cli tool even if
possible and this results in a chunked transfer encoding. Test 173 is
updated accordingly.

Additional mime-specific tests.
Existing tests updated to reflect small differences (Expect: 100-continue,
data size change due to empty lines, etc).
Option -F headers= keyword added to tests.
test1135 disabled until the entry point order change is resolved.
New example smtp-mime.
Examples postit2 and multi-post converted from form API to mime API.

Extended -F option syntax to support multipart mail messages.
-F keyword headers= added to include custom headers in parts.
Documentation upgraded.

Available in HTTP, SMTP and IMAP.
Deprecates the FORM API.
See CURLOPT_MIMEPOST.
Lib code and associated documentation.

Closes #1849

... so that users can actually write code based on the man page alone,
not having to read the header file.

./sslbackend.c:58:3: warning: else after closing brace on same line (BRACEELSE)
   } else if(isdigit(*name)) {
   ^
./sslbackend.c:62:3: warning: else after closing brace on same line (BRACEELSE)
   } else
   ^

it is a one time *set*, not necessarily a one time use... it can be
called again if the first call failed or just listed the alternatives.

clarify that the available backends are the ones this build supports

plus add some formatting

Reported-by: Rich Gray
Bug: https://curl.haxx.se/mail/lib-2017-08/0119.html

Closes #1837