Move move .emacs.d out of configs/shared

Moving all of my Emacs-related files into their own directory at the root of
this repository.

emacs/.emacs.d/wpc/prelude.nix

@@ -0,0 +1,11 @@
+{ pkgs ? import (builtins.fetchTarball
+  "https://github.com/tazjin/depot/archive/master.tar.gz") {} }:
+
+# Ciruclar dependency warning: list.nix depends on prelude.nix, which depends on
+# list.nix.
+pkgs.writeElispBin {
+  name = "prelude";
+  # If this can build with epkgs.ht, remove `(require 'ht)`.
+  deps = epkgs: [ epkgs.s epkgs.dash epkgs.f ./string.nix ./list.nix ];
+  src = ./prelude.el;
+}