Add GTK-Doc

packages/gtk_doc.rb

+require 'package'
+
+class Gtk_doc < Package
+  description 'GTK-Doc is a project which was started to generate API documentation from comments added to C code.'
+  homepage 'https://www.gtk.org/gtk-doc'
+  version '1.26'
+  source_url 'https://github.com/GNOME/gtk-doc/archive/GTK_DOC_1_26.tar.gz'
+  source_sha256 'f0bcb1ff8268136fdbf426d7862f4f092e70b24a73632cfe0a3d31ed0d924b5c'
+
+  depends_on 'python3'
+  depends_on 'python27'
+  depends_on 'autoconf'
+  depends_on 'automake'
+  depends_on 'libxml2'
+  depends_on 'libxslt'
+  depends_on 'docbook'
+  depends_on 'docbook_xml'
+  depends_on 'docbook_xsl'
+
+  def self.build
+    system 'pip3 install six'
+    system 'pip install six'
+    system './autogen.sh --with-xml-catalog=/usr/local/etc/xml/catalog'
+    system './configure --with-xml-catalog=/usr/local/etc/xml/catalog'
+    system 'make'
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end