Add NSM Addon Updater integration

Adding NSM Addon updater support in your addon is easy. Create a config.php file in the root folder of your addon and add:

<?php
$config['name']='Addon Name';
$config['version']='0.1.0';
$config['nsm_addon_updater']['versions_xml']='http://site.com/versions.xml';

The 'versions_xml' url should point to a valid RSS 2.0 XML feed that lists individual versions of your addon as `<items>`. There is only one additional required tag: `<ee_addon:version>1.0.0b1</ee_addon:version>` which is used for version comparison.

Example RSS 2.0 XML Feed

<?xml version="1.0" encoding="utf-8"?>
<rss 
  version="2.0"
  xmlns:ee_addon="http://ee-garage.com/nsm_addon_updater"
>
  <channel>
    <title>NSM Addon Updater Changelog</title>
    <link>http://site.com/nsm_addon_updater/appcast.xml</link>
    <description>Most recent changes with links to updates.</description>
    <item>
      <title>Version 0.1.0</title>
      <!-- Additional tag required for NSM Addon Updater -->
      <ee_addon:version>0.1.0</ee_addon:version>
      <link>http://site.com/nsm_addon_updater</link>
      <pubDate>Wed, 09 Jan 2006 19:20:11 +0000</pubDate>
      <description><![CDATA[
        <ul>
          <li>Initial Release</li>
        </ul>
      ]]></description>
      <enclosure 
        url="http://yourdomain.com/addon.zip"
        length="1623481"
        type="application/zip"
      />
    </item>
  </channel>
</rss>

Each feed is individually cached so that the CURL calls don't stall the loading of the CP.