Beginnings of config for Darwin machines

Split out a platforms/ directory with a linux.nix and darwin.nix, and
starting splitting things out between the two

home/modules/common.nix

@@ -0,0 +1,38 @@
+{ config, lib, pkgs, ... }:
+
+{
+  imports = [
+    ../modules/shell.nix
+    ../modules/development.nix
+    ../modules/emacs.nix
+    ../modules/vim.nix
+    ../modules/tarsnap.nix
+  ];
+
+  nixpkgs.config.allowUnfree = true;
+  programs.password-store.enable = true;
+
+  impure.clonedRepos.passwordStore = {
+    github = "glittershark/pass";
+    path = ".local/share/password-store";
+  };
+
+  home.packages = with pkgs; [
+    htop
+    killall
+    bind
+    zip unzip
+    tree
+    ncat
+
+    gnupg
+    keybase
+    openssl
+
+    # Nix things
+    nixfmt
+    nix-prefetch-github
+    nix-review
+    cachix
+  ];
+}