Don't add empty string value to valueless attributes
Merge pull request #148 from remcohaszing/gh-pages

Don't add empty string value to valueless attributes
Move js, css to assets. Create benchmarks folder.
Fix grunt
Disable clean-css' advanced optimizations by default. Closes #147
Escape closing script tag. Closes #142
Update uglify.js to v2.4.13.

The file is generated with `uglifyjs --self -o uglify.js`.
Update _config.yml.