Closes #544

Closes #543

Closes #522

Make (most) example snippets use the example.com domain instead of the
random ones picked and used before. Some of those were probably
legitimate sites and some not. example.com is designed for this purpose.

Closes #754

It's a bad idea to send your passwords anywhere, especially over HTTP.
Modified example to send a picture instead.

Fixes #752

Now sorted into categories and organized in the same style we do the
TODO document. It will make each issue linked properly on the
https://curl.haxx.se/docs/knownbugs.html web page.

The sections should make it easier to find issues and issues related to
areas of the reader's specific interest.

Bug: https://github.com/curl/curl/issues/536


Reported-by:  <eXeC64@users.noreply.github.com>

Due to their age (we don't fully know if they actually remain) and lack
of detail - very few people will bother to find out what they're about
or work on them. If people truly still suffer from any of these, I
assume they will be reported again and then we'll deal with them.

72. "Pausing pipeline problems."
  https://curl.haxx.se/mail/lib-2009-07/0214.html

70. Problem re-using easy handle after call to curl_multi_remove_handle
  https://curl.haxx.se/mail/lib-2009-07/0249.html

68. "More questions about ares behavior".
  https://curl.haxx.se/mail/lib-2009-08/0012.html

... to please the new, slightly picker, checksrc.pl

We never made a 7.25.1 release

The define is not in our name space and is therefore not protected by
our API promises.

It was only really used by libcurl internals but was mostly erased from
there already in 8aabbf5f (March 2015). This is supposedly the final
death blow to that define from everywhere.

As a side-effect, making sure _MPRINTF_REPLACE is gone and not used, I
made the lib tests in tests/libtest/ use curl_printf.h for its redefine
magic and then subsequently the use of sprintf() got banned in the tests
as well (as it is in libcurl internals) and I then replaced them all
with snprintf().

In the unlikely event that any users is actually using this define and
gets sad by this change, it is very easily copied to the user's own
code.

Supports HTTP/2 over clear TCP

- Optimize switching to HTTP/2 by removing calls to init and setup
before switching. Switching will eventually call setup and setup calls
init.

- Supports new version to “force” the use of HTTP/2 over clean TCP

- Add common line parameter “--http2-prior-knowledge” to the Curl
  command line tool.

... load file specified as argument.

Closes #733

... to make them appear as links on the html version.

Closes #677

Closes #729
Closes #728

Add ALPN support for schannel. This allows cURL to negotiate
HTTP/2.0 connections when built with schannel.

Closes #724

... and update the coming release dates a bit

Bug: https://github.com/curl/curl/issues/685