Fix some incorrect links

I had some issues with the links pointing to the main page in the sidebar. They would always point to the current page. I fixed this by changing site.baseurl to site.url in the definition of these two links (title and Home) in the file _includes/sidebar.html.
Also, as I was looking for a solution to that problem, I found that all url’s in Jekyll should really be defined as { { site.baseurl } }{ { post.url } }, and the variable baseurl should be left empty, instead of /. I found this page to be pretty useful.