refactor: Fix a variety of filepaths for repo relayouting

This fixes readTree and the various project builds, as well
as (hopefully) most documentation links inside of the projects.

overrides/writeElispBin/default.nix

@@ -0,0 +1,23 @@
+{ pkgs, ... }:
+
+{ name, src, deps ? (_: []), emacs ? pkgs.third_party.emacs26-nox }:
+
+let
+  inherit (pkgs.third_party) emacsPackagesNg emacsPackagesNgGen writeTextFile;
+  inherit (builtins) isString toFile;
+
+  finalEmacs = (emacsPackagesNgGen emacs).emacsWithPackages deps;
+
+  srcFile = if isString src
+    then toFile "${name}.el" src
+    else src;
+in writeTextFile {
+  inherit name;
+  executable = true;
+  destination = "/bin/${name}";
+
+  text = ''
+    #!/bin/sh
+    ${finalEmacs}/bin/emacs --batch --no-site-file --script ${srcFile} $@
+  '';
+}