AfterUploadTask > Sitemap Ping

This add's a AfterUploadTask class, with a sitemap pinger activity. 
This is to ping both Google and Bing after an upload to S3 has been successful.

It is to be used in conjunction with the Sitemap generator https://github.com/kinnetica/jekyll-plugins .
Simply add url: <url>, sitemap: sitemap.xml to s3_website.cfg
I've made url seperate from sitemap config options for later use.

I'm not a Ruby coder so I appreciate any comments, unfortunately my test skills on Ruby are seriously lacking so there are no unit tests for the changes.