Allow updating or uninstalling packages

[kylewlacy]

brioche install lets you install packages into a "global" (per-user) directory (default: ~/.local/share/brioche/installed). But there's no way to uninstall a package once installed, nor an easy way to update existing packages. We should add a way to update, uninstall, and list packages installed with brioche install

Unfortunately, fixing this won't be retroactive. brioche install is dead-simple today, and it dumps the output of a build directly into ~/.local/share/brioche/installed without saving any extra metadata during the process. That means for existing packages installed with Brioche, we won't be able to determine which packages the user actually installed!

[kylewlacy]

You can also install packages locally, e.g. using brioche install -p ./packages/ripgrep. This gets a bit trickier for management, and it's not clear to me how (or if) we should handle updates for such packages...