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

Link to list of 3rd party library licenses in about window

remove openal from MacPorts deps

OpenAL support was removed by VS-all  #440, replaced by PortAudio.

voronoi merger inherits mask merger, make destructor virtual

Fix GLEW

Create sponsoring button

Update build doc for Mac

Linux pkg sys

unused lambda capture

Now we can only use mac ports or homebrew