Gtk3 joystick code testing for VICE, or rather Linux joystick code testing which may someday land in VICE.

Currently this code is completely unusable. Widgets are unfinished/missing, the joystick polling is backwards and the Meson/Ninja stuff is missing any checks for non-gtk3 headers. It also needs a lot more CFLAGS to adhere to my 'standard'.

To build this meson/ninja is required. See https://mesonbuild.com/ for details.

Basically make sure pip3 is installed (the python3 package manager) and then do pip3 install meson, this should pull in all required stuff for Meson/Ninja. I personally run that with sudo so it gets installed system-wide.

Once that is done, run meson builddir, which runs meson and creates a separate builddir (meson requires this). When that succeeds, cd builddir and ninja to build. If all goes well, the binary can be run with ./gtk3-joytester.