LIJI32
add appimage build target
This is a simple attempt at getting AppImages to work
feedback is definitely needed and I mainly wanted to get this out the door for now since this would allow for simple binary releases that target Linux.
This uses linuxdeploy which isn't package anywhere (that I am aware of) and is mainly distributed as an AppImage, so perhaps it would be better to put the tool into a variable that is definable when invoking make.
FreeDesktop/AppIcon/512x512.png has been symlinked to FreeDesktop/sameboy.png simply because the linuxdeploy needs the icon file and the icon variable in the desktop file to be the same.
the resource_path() function has been patched to check for the APPDIR environment variable that is specified here
https://docs.appimage.org/packaging-guide/environment-variables.html
If needed I can include a Github Actions workflow that builds an AppImage for releases
