Add the mg editor

packages/mg.rb

+require 'package'
+
+class Mg < Package
+  description 'mg is the portable version of the mg editor from OpenBSD'
+  homepage 'https://devio.us/~bcallah/mg/'
+  version '20170917'
+  source_url 'https://devio.us/~bcallah/mg/mg-20170917.tar.gz'
+  source_sha256 'def9237a89ec6a14241abaf12714bc5fcb3b0e2f8d9d466ff7561628d35b7ff1'
+
+  depends_on 'ncurses'
+
+  def self.build
+    system "CFLAGS=-I/usr/local/include/ncurses make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end