* Adds a script to clone and build FFmpeg as well as
to configure and build mpv itself. Currently only used
for macOS and contain hard-coded macOS specific options.
* Still works with the Linux containers.
* Moves our language back to "c" from "generic"
* Defines our Linux distribution as "bionic" to get the latest
Ubuntu base distribution to be the runner for our containers.
* Adds the homebrew add-on for macOS package installation for
dependencies. Installs everything required but FFmpeg, as we want
to have our own FFmpeg snapshots.
Jan Ekström