gnu: Add emacs-gitpatch.

By the way, “gitpatch.el” says different version than release tarball.
Do I need to ask a developer?
--8<---------------cut here---------------start------------->8---
;; Author: Feng Shu <tumashu@163.com>
;; Homepage: https://github.com/tumashu/gitpatch
;; Keywords: convenience
;; Package-Requires: ((emacs "24.3"))
;; Version: 0.10
--8<---------------cut here---------------end--------------->8---

>From 9eddf07fa401468738c2f48a25e51ddef2a3ceed Mon Sep 17 00:00:00 2001
From: Oleg Pykhalov <go.wigust@gmail.com>
Date: Sat, 29 Jul 2017 14:22:48 +0300
Subject: [PATCH] gnu: Add emacs-gitpatch.

* gnu/packages/emacs.scm (emacs-gitpatch): New variable.

Signed-off-by: Arun Isaac <arunisaac@systemreboot.net>

gnu/packages/emacs.scm

@@ -5262,3 +5262,24 @@ editing RPM spec files.")
 the last git commit message for the current line.  This uses git-blame
 internally.")
     (license license:gpl3+)))
+
+(define-public emacs-gitpatch
+  (package
+    (name "emacs-gitpatch")
+    (version "0.5.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "https://github.com/tumashu/gitpatch/archive/"
+                           "v" version ".tar.gz"))
+       (file-name (string-append name "-" version ".tar.gz"))
+       (sha256
+        (base32
+         "1yj6pmic541lcnscjin300k380qp9xdfprs55xg1q57jrkq6f6k7"))))
+    (build-system emacs-build-system)
+    (home-page "https://github.com/tumashu/gitpatch")
+    (synopsis "Mail git patch from Emacs")
+    (description "@code{emacs-gitpatch} lets users easily send git patches,
+created by @code{git format-patch}, from @code{magit}, @code{dired} and
+@code{ibuffer} buffers.")
+    (license license:gpl3+)))