fix for categories not displayed

minor edit - if condition should be on page.categories & not on post.categories
Fix for sharing URLs

page.url gives the URL of the Post without the domain, but with a leading slash, e.g.  /2014/01/05/my-post.html

site.url is added so that domain is included while sharing. The value must be set in _config.yml file
Merge pull request #8 from nrbafna/master

Fix for categories not displayed