feat(third_party/lisp): Check in drakma HTTP client & deps

This HTTP client has much fewer dependencies than some of the other
ones I've seen, and it'll be good enough for my demo purposes.

third_party/lisp/drakma.nix

@@ -0,0 +1,35 @@
+# Drakma is an HTTP client for Common Lisp.
+{ pkgs, ... }:
+
+let src = pkgs.third_party.fetchFromGitHub {
+  owner = "edicl";
+  repo = "drakma";
+  rev = "87feb02bef00b11a753d5fb21a5fec526b0d0bbb";
+  sha256 = "01b80am2vrw94xmdj7f21qm7p5ys08mmpzv4nc4icql81hqr1w2m";
+};
+in pkgs.nix.buildLisp.library {
+  name = "drakma";
+  deps = with pkgs.third_party.lisp; [
+    asdf
+    chipz
+    chunga
+    cl-base64
+    cl-plus-ssl
+    cl-ppcre
+    flexi-streams
+    puri
+    usocket
+  ];
+
+  srcs = map (f: src + ("/" + f)) [
+    "drakma.asd" # Required because the system definition is used
+    "packages.lisp"
+    "specials.lisp"
+    "conditions.lisp"
+    "util.lisp"
+    "read.lisp"
+    "cookies.lisp"
+    "encoding.lisp"
+    "request.lisp"
+  ];
+}