The possibility of spawning main interfaces after the start of libvlc
was removed in VLC 4.0.

Ref vlc!4865

Setup the libvlc dependency so that depending on libvlcpp works
correctly.

This is a GNU function. We have the tool in C++ to concatenate strings
and integers.

Fixes #14

configure.ac:18: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:18: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
configure.ac:18: the top level
configure.ac:22: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:22: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
configure.ac:22: the top level

Cancelling usage have been merged with `thumbnailRequestDestroy`.

Refs vlc!3153

Replace libvlc_audio_XXX_channel with libvlc_audio_XXX_stereomode

The values come from an enum and are mostly compatible with older values.

Add mixMode/setMixMode functions.

The media isn't constructed with an instance anymore, but takes the
instance as a parameter later on when needed

The error dialog callback is now a separated callback

It's part of the dialog API

After vlc!1512 is merged.

The very latest git version of libc++ has reduced the amount of
transitive includes of <algorithm>.

The module parameter has been removed in
vlc@fd345221

So we just keep the outputDeviceSet() variant that didn't have the module
parameter.

Use a newer image of vlc 4.0 that has this API change.

Since we're now using an async stop function, we might be freeing the
buffer while it's still being used.
Instead, release it automatically after the instance itself has been
released since we're guaranteed to have joined all threads at this point

Following vlc!1225