Adds the necessary gem and configuration directives for generating a sitemap.xml file in the project

The sitemap.xml file when uploaded to Google Webmaster Tools should help improve the SEO because the file will be regenerated on every site build & publish. The updated file will tell Google that there is new content to indexed.
Merge pull request #56 from scottelundgren/sitemap

Adds the necessary gem and configuration directives for generating a sit...