remove _site/ dir from gh-pages branch

* _site/ will be generated by github pages automatically
replace deprecated pygments option with highlither
replace url with baseurl in config file
update urls to fix rendering

* use {{ baseurl }} in templates to allow testing the site locally
before pushing to github
* mostly recommendations from http://jekyllrb.com/docs/github-pages/#project-page-url-structure
feed.xml: replace with updated jekyll's template