Remove using of `site.github.url`

Hi, because #46 the site style and some links are broken, so, I do not like to do it, but I am hard coding references to temporally fix it. I did not have time to research for another solution.

The problem with this fix is that it will not work on personal forks like http://andresmoschini/makingsense.github.io/migration-to-git/

I need the site working today at 3 PM ARG, so, if nobody comment I will merge it before.