Add support for Flatpak and AppImage

[m3thm4th]

Snap is Canonical's monopoly and the backend is not FOSS. It's also strictly dependant on systemd. Flatpak and AppImage are more open universal package managers.

[ShrirajHegde]

AppImage is a bundled SquashFS image, it has no package management.

Static binaries are better most of the time than AppImage whenever it's possible, especially for a CLI program.