Faster XML generation for Ruby on Rails.

Calling #to_xml on large data sets can use quite a lot of cpu time.
This plugin is meant to speed up the generation to XML documents that are based 
on active record data.

Technically, this plugin re-implements Array#to_xml and 
ActiveRecord::Base#to_xml. To speed up the creation of XML output, this plugin
uses the gem 'libxml-ruby' which provides a native binding to libxml.