Add docbook package

packages/docbook.rb

+require 'package'
+
+class Docbook < Package
+  description 'DocBook is an XML vocabulary that lets you create documents in a presentation-neutral form that captures the logical structure of your content.'
+  homepage 'http://docbook.sourceforge.net/'
+  version '1.79.1'
+  source_url 'https://downloads.sourceforge.net/project/docbook/docbook-xsl/1.79.1/docbook-xsl-1.79.1.tar.bz2'
+  source_sha1 '7487b2acc7106253bb77fcddc7e1a9788601ad23'
+
+  def self.install
+    system "mkdir -p #{CREW_DEST_DIR}/usr/local/docbook"
+    system "cp -r . #{CREW_DEST_DIR}/usr/local/docbook"
+  end
+end