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

LINUX_PKG is now the only option

use a docker image for CI

we need this to make later versions of CUDA compile