When the default format is used and export fails, format was NULL

Fixes https://github.com/cacalabs/libcaca/issues/65

Patch from Fedora
https://src.fedoraproject.org/rpms/libcaca/blob/rawhide/f/libcaca-0.99.beta20-c99.patch

This is an internal function that can not be used in this sample code.
Easiest is to duplicate it.

Fixes https://github.com/cacalabs/libcaca/issues/67

getpid() or _getpid() are not available in UWP builds [1] but we can use
GetCurrentProcessId() instead.

[1] https://learn.microsoft.com/en-us/cpp/cppcx/crt-functions-not-supported-in-universal-windows-platform-apps#unsupported-crt-functions

The API is always available in Win8+ even in UWP builds, unlike CreateFileW.
The API is pretty much the same. CONOUT is also supported [1].

[1] https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2#consoles

If the environment forces the UNICODE define it will use the wrong call.

It's already defined properly.

If the system allows newer API's we should downversion it.

Patch courtesy of Jakub Bogusz.

Patch courtesy of Jakub Bogusz.

Fix py img2txt

Add support for IPv6 to cacaserver

Disable cppunit  tests by default, honor --enable-cppunit

Bold/italic attribute support for export to svg

slang driver: enable utf8 auto-detection (bug fix)

These were all caused by sprintf() appending a null char that was not actually used.
Fixes CVE-2021-30498 and CVE-2021-30499.

Fixes: #52 (CVE-2021-3410)

Fixes: #42

Fixes: #38 (CVE-2018-20546)
Fixes: #39 (CVE-2018-20547)

Fixes: #37 (CVE-2018-20545)
Fixes: #40 (CVE-2018-20548)
Fixes: #41 (CVE-2018-20549)

Fixes: #36 (CVE-2018-20544)

Hide private symbols (issue #33).

The slang internal auto-detection of utf8 is only executed by a call to
SLutf8_enable(-1).