Attempt to package CL unit testing with Nix

My first foray trying to package Common Lisp with Nix. I'm using @tazjin's
buildLisp and other libraries, all of which I'm importing as `tpkgs`, and all of
which have been a tremendous boon to my productivity.

common-lisp/default.nix

@@ -0,0 +1,13 @@
+{ tpkgs ? (import (builtins.fetchGit "https://git.tazj.in/") {}), ... }:
+
+tpkgs.nix.buildLisp.program {
+  name = "unit-testing";
+
+  deps = with tpkgs.third_party.lisp; [
+    (import ./prove.nix {})
+  ];
+
+  srcs = [
+    ./unit-testing.lisp
+  ];
+}