Proposal: Don't use ~/.zig, use eg. `~/.zigup` instead

I don't want this to sound too negative, but at least on GNU/Linux-based systems, it's pretty much established that applications only "own" directories named the same as the app itself. Eg. vim owns `~/.vim` or `~/.config/vim` but not something else. Personally I tend to avoid tools and apps that don't follow the convention, because it adds additional mental load when managing them, and also can potentially lead to conflicts with another applications. So the proposal is that `zigup` should: * use `$HOME/.zigup` * or better, use XDG conventions, ie. combination of: * `$HOME/.config/zigup` for permanent, shared config, * `$HOME/.local/share/zigup` for local files, * `$HOME/.cache/zigup` for cache, etc. I realize that cost of moving a path can be high, but it's better to do it sooner than later.