attempt MACPORTS OpenCV4 build. weird lade and with opencv_contrib also openjpeg dependencies dragged in by OpenCV4. still doesn't link the OpenCV API properly

* Use nice container feature of github actions
* Remove automated builds for CUDA 8 and 9

OpenCV4 support : change old C definition to standard c++ one in use
the old definition still exist in imgproc.c_types.h

add camorah info and download link to README

Fixes for Mac Package

The change is needed as MSVC doesn't allow for a vector of a map
of a non-copyable object.

We can't use a list, as apparently several calls to loadAudio need
to write the blocks of different audio groups into the same position
in the output vector. std::list doesn't have random access.

Using a map now, so we can keep the previous behavior. The int64_t key
is only used in construction, and can be disregarded by the loading
code.

Audio::Samples are a move-only class, they can't be copied.

Using this non-copyable class in a std::vector<std::map<..>> does not
compile in Visual Studio 2017, see e.g.:

https://stackoverflow.com/questions/58700780/vector-of-maps-of-non-copyable-objects-fails-to-compile-in-msvc

Replacing the use of vector with list, which does compile.

MacPorts: ensure ffmpeg is installed w/ rtmpdump & non-free codecs