Add gitstats formula

The author will not create release tags, so we must use the HEAD of the
repository instead.

Closes hoxu/gitstats#29
Refs Homebrew/legacy-homebrew#14418
Refs Homebrew/legacy-homebrew#25447

gitstats.rb

@@ -0,0 +1,18 @@
+class Gitstats < Formula
+  desc "git history statistics generator"
+  homepage "http://gitstats.sourceforge.net/"
+  head "https://github.com/hoxu/gitstats.git"
+
+  depends_on "gnuplot"
+
+  def install
+    system "make", "install", "PREFIX=#{prefix}"
+
+    system "make", "man"
+    man1.install "doc/gitstats.1"
+  end
+
+  test do
+    system "#{bin}/gitstats"
+  end
+end