AfterUploadTask class > sitemap pinger

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: , 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.