Heavily inspired by these:
- https://github.com/zmre/mac-nix-simple-example
- https://github.com/dustinlyons/nixos-config

This mirrors what is in link/nix/vimrc

With the exception of 1Password, the changes here are for apps not
available on darwin. 1Password was changed around because it must be
installed directly in /Applications to run. I filed this bug report
about the issue: NixOS/nixpkgs#254944

The Nix version doesn't include the gui bits.

Now, the OS icon is only rendered when in a WSL environment as it isn't
that useful or easy to read the rest of the time.

The folder icon was removed from the path part of the prompt because it,
too, was hard to read and served no helpful purpose.

Colors were cleaned up so that names are used everywhere and unused bits
were removed.

With help from others, I can now pull the theme file from the repo it
lives in instead of embedding it here!