Add deferred derivation

pkgs/top-level/emacs-packages.nix

@@ -263,6 +263,29 @@ let self = _self // overrides;
     meta = { license = gpl3Plus; };
   };
 
+  deferred = melpaBuild rec {
+    version = "0.3.2";
+    pname = "deferred";
+
+    src = fetchFromGitHub {
+      owner = "kiwanami";
+      repo = "emacs-${pname}";
+      rev = "896d4b53210289afe489e1ee7db4e12cb9248109";
+      sha256 = "0ysahdyvlg240dynwn23kk2d9kb432zh2skr1gydm3rxwn6f18r0";
+    };
+
+    meta = {
+      description = "Simple asynchronous functions for emacs-lisp";
+      longDescription = ''
+        deferred.el provides facilities to manage asynchronous tasks.
+        The API and implementations were translated from JSDeferred (by cho45)
+         and Mochikit.Async (by Bob Ippolito) in JavaScript.
+      '';
+      homepage =  https://github.com/kiwanami/emacs-deferred;
+      license = gpl3Plus;
+    };
+  };
+
   diminish = melpaBuild rec {
     pname   = "diminish";
     version = "0.44";