Attempt to inject dependencies into blog/server

- We need the markdown files, to be in the /nix/store and the server needs to be
  aware of there location.
- Since we're dependending on `pandoc`, our server needs to know about it too.

For both of these cases -- especially for the latter case -- I imagine there may
be a more idiomatic way of doing this.

blog/default.nix

@@ -1,15 +1,27 @@
 {
+  pkgs ? import <nixpkgs> {},
   depot ? import <depot> {},
   universe ? import <universe> {},
   ...
 }:
 
-depot.nix.buildLisp.program {
+let
+  injectedPosts = pkgs.writeText "posts.lisp" ''
+    (in-package #:server)
+    (setq *path-to-posts* "${./posts}")
+  '';
+  injectedExecutables = pkgs.writeText "executables.lisp" ''
+    (in-package #:server)
+    (setq *pandoc-bin* "${pkgs.pandoc}/bin/pandoc")
+  '';
+in depot.nix.buildLisp.program {
   name = "server";
   deps = with depot.third_party.lisp; [
     hunchentoot
   ];
   srcs = [
     ./src/server.lisp
+    injectedPosts
+    injectedExecutables
   ];
 }