Modify zenburn theme according to zenburn-emacs

* Replace all black color fonts by default font
* Update colors according to zenburn theme
* https://github.com/bbatsov/zenburn-emacs
Mimetype for RSS feed is application/rss+xml, not application/atom+xml, fixes #94
Added article:author open graph tag and showing author/category on article is now configurable
Merge pull request #95 from puzan/zenburn_theme

Modify zenburn theme according to zenburn-emacs
Merge branch 'master' of https://github.com/DandyDev/pelican-bootstrap3

Conflicts:
	templates/includes/article_info.html