use sitemap not index

Org-mode's index is not what you want for a homepage/index of blog
posts, the sitemap feat is much better suited. http://orgmode.org/manual/Sitemap.html
added css

fontlock.css: generated from output-font-lock-css
shared.css: some custom styles
change gitignore to ignore orgx files but not whole blog
refer to static files with root url, avoid issues with multiple levels

Alternative to: http://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html#sec-6